ci: clone godot-cpp directly so GDExtension build can find it

.github/CONTRIBUTING.md

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+# Contributing to RC-Flight-Sim
+
+Thank you for your interest in contributing!
+
+Please read the full contribution guide in [docs/contributing.md](../docs/contributing.md).
+
+## Quick Links
+
+- [Bug Reports](.github/ISSUE_TEMPLATE/bug_report.md)
+- [Feature Requests](.github/ISSUE_TEMPLATE/feature_request.md)
+- [Aircraft Creation Guide](../docs/aircraft_creation.md)
+- [Scenery Creation Guide](../docs/scenery_creation.md)
+- [Build Instructions](../docs/build_instructions.md)
+
+## Summary
+
+1. Fork the repo and create a feature branch.
+2. Follow the coding standards in `docs/contributing.md`.
+3. Open a pull request against `main` with a clear description.
+4. All contributions are licensed under MIT (code) or CC0/CC-BY-SA (art assets).

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: "🐛 Bug Report"
+about: "Report a problem or unexpected behaviour"
+title: "[BUG] "
+labels: ["bug", "needs-triage"]
+assignees: []
+---
+
+## Summary
+
+<!-- One-line description of the bug -->
+
+## Environment
+
+| Field | Value |
+|-------|-------|
+| OS | Windows / Linux / macOS / Android / Web |
+| Godot Version | e.g. 4.2.2 |
+| RC-Flight-Sim Version | e.g. 0.1.0 or commit hash |
+| Controller | e.g. Flysky FS-i6 USB dongle / Xbox controller / Keyboard |
+| Rendering Backend | GL Compatibility / Forward+ / Mobile |
+
+## Steps to Reproduce
+
+1. 
+2. 
+3. 
+
+## Expected Behaviour
+
+<!-- What should happen -->
+
+## Actual Behaviour
+
+<!-- What actually happens – include error messages, screenshots, video if possible -->
+
+## Console Output / Log
+
+```
+Paste Godot console output here
+```
+
+## Additional Context
+
+<!-- Any other context that may help diagnose the issue -->

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: "✨ Feature Request"
+about: "Suggest a new feature or improvement"
+title: "[FEATURE] "
+labels: ["enhancement"]
+assignees: []
+---
+
+## Problem / Motivation
+
+<!-- Describe the problem this feature would solve or the opportunity it addresses -->
+
+## Proposed Solution
+
+<!-- Describe what you'd like to happen. Be as specific as possible. -->
+
+## Alternatives Considered
+
+<!-- Have you considered other approaches? Why is your proposed solution better? -->
+
+## Design Pillars Alignment
+
+Check all that apply:
+
+- [ ] Accessible & Lightweight
+- [ ] Physics Realism
+- [ ] Universal Controller Support
+- [ ] Diverse Flying Environments
+- [ ] Multiple Viewpoints
+- [ ] Modular & Extensible
+
+## Additional Context
+
+<!-- Screenshots, mockups, references to other simulators, papers, etc. -->

.github/workflows/build.yml

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+name: Build & Export RC-Flight-Sim
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+  workflow_dispatch:
+
+env:
+  GODOT_VERSION: "4.2.2"
+  EXPORT_NAME:   "RC-Flight-Sim"
+  PROJECT_PATH:  "godot_project"
+
+jobs:
+  # ---------------------------------------------------------------------------
+  # Build the JSBSim GDExtension (stub / kinematic mode, no JSBSim deps)
+  # ---------------------------------------------------------------------------
+  build-extension:
+    name: Build GDExtension (${{ matrix.os }})
+    permissions:
+      contents: read
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: ubuntu-22.04
+            lib_suffix: .so
+            cmake_extra: ""
+          - os: windows-2022
+            lib_suffix: .dll
+            cmake_extra: ""
+          - os: macos-13
+            lib_suffix: .dylib
+            cmake_extra: "-DCMAKE_OSX_ARCHITECTURES=x86_64;arm64"
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: recursive
+
+      - name: Fetch godot-cpp (matching Godot ${{ env.GODOT_VERSION }})
+        run: |
+          if [ ! -f godot-cpp/CMakeLists.txt ]; then
+            rm -rf godot-cpp
+            git clone --depth 1 --branch godot-4.2 https://github.com/godotengine/godot-cpp godot-cpp
+          fi
+        shell: bash
+
+      - name: Cache CMake build
+        uses: actions/cache@v4
+        with:
+          path: godot_project/addons/jsbsim_gdextension/build
+          key: ${{ runner.os }}-cmake-${{ hashFiles('godot_project/addons/jsbsim_gdextension/**') }}
+
+      - name: Configure CMake (stub – no JSBSim)
+        run: |
+          cmake -B godot_project/addons/jsbsim_gdextension/build \
+            -DCMAKE_BUILD_TYPE=Release \
+            -DJSBSIM_ENABLED=OFF \
+            -DGODOT_CPP_DIR=${{ github.workspace }}/godot-cpp \
+            ${{ matrix.cmake_extra }} \
+            godot_project/addons/jsbsim_gdextension
+        shell: bash
+
+      - name: Build
+        run: cmake --build godot_project/addons/jsbsim_gdextension/build --config Release -j4
+        shell: bash
+
+      - name: Upload extension binary
+        uses: actions/upload-artifact@v4
+        with:
+          name: extension-${{ runner.os }}
+          path: godot_project/bin/jsbsim_gdextension${{ matrix.lib_suffix }}
+          if-no-files-found: warn
+
+  # ---------------------------------------------------------------------------
+  # Export Godot project for all platforms
+  # ---------------------------------------------------------------------------
+  export:
+    name: Export (${{ matrix.platform }})
+    permissions:
+      contents: read
+    runs-on: ubuntu-22.04
+    needs: build-extension
+    strategy:
+      fail-fast: false
+      matrix:
+        platform:
+          - name: Windows
+            export_preset: "Windows Desktop"
+            output_dir:    "build/windows"
+            output_file:   "RC-Flight-Sim.exe"
+          - name: Linux
+            export_preset: "Linux/X11"
+            output_dir:    "build/linux"
+            output_file:   "RC-Flight-Sim.x86_64"
+          - name: macOS
+            export_preset: "macOS"
+            output_dir:    "build/macos"
+            output_file:   "RC-Flight-Sim.zip"
+          - name: Android
+            export_preset: "Android"
+            output_dir:    "build/android"
+            output_file:   "RC-Flight-Sim.apk"
+          - name: Web
+            export_preset: "Web"
+            output_dir:    "build/web"
+            output_file:   "RC-Flight-Sim.html"
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Download extension binaries
+        uses: actions/download-artifact@v4
+        with:
+          pattern: extension-*
+          path: godot_project/bin/
+          merge-multiple: true
+
+      - name: Setup Godot ${{ env.GODOT_VERSION }}
+        uses: chickensoft-games/setup-godot@v2
+        with:
+          version: ${{ env.GODOT_VERSION }}
+          use-dotnet: false
+          include-templates: true
+
+      - name: Create output directory
+        run: mkdir -p ${{ matrix.platform.output_dir }}
+
+      - name: Export (${{ matrix.platform.name }})
+        run: |
+          godot --headless \
+            --path ${{ env.PROJECT_PATH }} \
+            --export-release "${{ matrix.platform.export_preset }}" \
+            "${{ github.workspace }}/${{ matrix.platform.output_dir }}/${{ matrix.platform.output_file }}"
+
+      - name: Upload ${{ matrix.platform.name }} build
+        uses: actions/upload-artifact@v4
+        with:
+          name: ${{ env.EXPORT_NAME }}-${{ matrix.platform.name }}
+          path: ${{ matrix.platform.output_dir }}/
+
+  # ---------------------------------------------------------------------------
+  # Create a GitHub Release on version tags
+  # ---------------------------------------------------------------------------
+  release:
+    name: Create Release
+    permissions:
+      contents: write
+    runs-on: ubuntu-22.04
+    needs: export
+    if: startsWith(github.ref, 'refs/tags/v')
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Download all build artifacts
+        uses: actions/download-artifact@v4
+        with:
+          pattern: ${{ env.EXPORT_NAME }}-*
+          path: release/
+
+      - name: Zip each platform build
+        run: |
+          cd release
+          for dir in */; do
+            zip -r "${dir%/}.zip" "$dir"
+          done
+
+      - name: Create GitHub Release
+        uses: softprops/action-gh-release@v2
+        with:
+          files: release/*.zip
+          generate_release_notes: true
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

.gitignore

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+# Godot-specific
+.godot/
+*.uid
+*.import
+
+# Build artifacts
+bin/*.dll
+bin/*.so
+bin/*.dylib
+godot_project/addons/jsbsim_gdextension/build/
+
+# OS-specific
+.DS_Store
+Thumbs.db
+desktop.ini
+
+# IDE
+.vscode/
+.idea/
+*.suo
+*.user
+
+# Exports
+build/
+dist/
+*.exe.meta
+
+# Python bytecode (scons)
+__pycache__/
+*.pyc
+*.pyo
+
+# CMake
+CMakeFiles/
+CMakeCache.txt
+cmake_install.cmake
+Makefile
+*.cmake.user

.gitmodules

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+[submodule "godot_project/addons/terrain_3d"]
+	path = godot_project/addons/terrain_3d
+	url = https://github.com/TokisanGames/Terrain3D
+
+[submodule "godot-cpp"]
+	path = godot-cpp
+	url = https://github.com/godotengine/godot-cpp
+	branch = godot-4.2
+
+[submodule "jsbsim"]
+	path = jsbsim
+	url = https://github.com/JSBSim-Team/jsbsim