Add frame limiter FPS offset

[kristofferR]

I've implemented the RTSS frame limiter offset requested in #177 :)

Sorry for pushing this here a little prematurely, Codex did it when I asked to "push the pr to my fork".

Summary

• Add frame_limiter_fps_offset so the automatic frame limiter can subtract FPS from the client-requested stream rate.
• Apply the offset to RTSS and NVIDIA limiter paths while keeping manual frame_limiter_fps_limit authoritative.
• Surface the setting in the Frame Limiter UI, per-app overrides, docs, and English locale files.

Validation

• git diff --check
• jq empty src_assets/common/assets/web/public/assets/locale/*.json
• bun run build

Ref #177

[chatgpt-codex-connector]

💡 Codex Review

Vibepollo/src/platform/windows/rtss_integration.cpp

Line 1022 in 7720a2f

return rtss_streaming_start(fps, 1);

Replace stale fps variable in RTSS refresh fallback

After changing rtss_streaming_refresh to accept (scaled_limit, denominator), this fallback still calls rtss_streaming_start(fps, 1), but fps is no longer defined in scope. On Windows builds, this causes a compile error in rtss_integration.cpp, blocking the build before runtime. The fallback should pass the new argument (likely scaled_limit) instead of the removed identifier.

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[kristofferR]

Validation update after pushing f19edf3f:

• Reopened this PR and confirmed the head is now f19edf3f00159d9a4f448a057e1ffbdf30a4749b.
• Configured build-dev with MSYS2 UCRT64, Debug, BUILD_TESTS=ON, SUNSHINE_ENABLE_WEBRTC=OFF, CUDA_FAIL_ON_MISSING=OFF.
• ninja -C build-dev completed successfully, including sunshine.exe, helper tools, tests/test_sunshine.exe, and the debug Web UI bundle.
• Launched the built sunshine.exe; the configuration UI served successfully at https://localhost:47990.
• ctest --test-dir build-dev --output-on-failure reported no registered CTest tests.
• Direct build-dev/tests/test_sunshine.exe --gtest_brief=1 currently fails existing Playnite sync/autosync, locale/config consistency, and mDNS naming expectations unrelated to the frame limiter build/run path.