Add AutoEq import browser for 0.8.0

[bhack]

Summary

• Add direct AutoEq profile search, curve preview, target/preamp/source details, and on-demand Equalizer APO preset import.
• Add AutoEq live compatibility checks, cache/release hardening, and 0.8.0 release metadata.
• Improve curve/output preset state labels exposed to the GNOME Shell extension.
• Add GSettings-backed window state and About dialog release notes.

Validation

• .venv/bin/python -m ruff check .
• .venv/bin/python -m ruff format --check .
• .venv/bin/python -m pytest -q
• .venv/bin/python tools/check_autoeq_live.py
• tools/run_release_preflight_container.sh
• local Flatpak build/install with flatpak run org.flatpak.Builder --user --install --force-clean --install-deps-from=flathub flatpak-build io.github.bhack.mini-eq.yaml
• .venv/bin/python tools/check_flatpak_runtime.py --app-ref io.github.bhack.mini-eq//master
• .venv/bin/python tools/check_live_ui_runtime.py --timeout 35 --cycles 3 --audio-duration 180

Before Release

• Wait for GitHub CI and CodeQL on this PR.
• Run one clean-permission background portal smoke in a real GNOME session.
• Decide whether to upload the changed GNOME Shell extension bundle.