feat: add baseline anti-cheat guards

[TJCurnutte]

Summary

/claim #2

Implements baseline anti-cheat protection for both required runtime paths:

• rewrites AntiCheat.cpp into a portable, buildable native guard with Windows debugger/process detection and POSIX fallback for local verification
• adds anti_cheat.py, a dependency-free Python monitor with debugger detection and suspicious process blocking
• adds regression tests for process normalization, suspicious process detection, debugger-first blocking, clean pass behaviour, and JSON output
• adds a short demo GIF at docs/javelin-anticheat-demo.gif

Acceptance criteria mapping

• Application exits when a debugger is detected: implemented in C++ (IsDebuggerPresent, CheckRemoteDebuggerPresent, PEB best-effort on MSVC, POSIX tracer fallback) and Python (sys.gettrace, Win32 IsDebuggerPresent, Linux TracerPid).
• Application exits when a suspicious process is found: implemented in both C++ and Python using the same conservative known-tool list.
• Works for both C++ client and Python monitor: both files are included, documented, and locally validated.

Demo

See docs/javelin-anticheat-demo.gif in this PR.

Validation

$ python3 -m unittest discover -s tests
........
----------------------------------------------------------------------
Ran 8 tests in 0.002s

OK

$ c++ -std=c++17 -Wall -Wextra -pedantic AntiCheat.cpp -o /tmp/javelin-anticheat-check
$ /tmp/javelin-anticheat-check
[Javelin AntiCheat] starting checks...
[Javelin AntiCheat] All clear. Continue.

$ git diff --check
# no output

Notes

This was implemented with AI assistance and manually reviewed before submission. I kept the patch scoped to the issue requirements and added tests so reviewers can verify behaviour without attaching a debugger or launching real cheat tools.

Fixes #2