Add ONNX subtitle and live audio translation

[mfkl]

Summary

• add packaged ONNX subtitle translation with bounded caching and deterministic model/runtime validation
• add live audio-to-subtitle translation with prepared and live-immediate playback modes
• keep the VLC audio callback allocation-free, make OpenVINO speech device selection explicit, and avoid GPU contention by forcing software video decode for GPU speech
• replace active translated captions instead of stacking overlapping text
• add benchmarks, Native AOT smoke checks, and a real VLC lifecycle workflow

Validation

• dotnet build vlclr.sln -c Release (0 warnings, 0 errors)
• dotnet test vlclr.sln -c Release --no-build --no-restore (496 passed)
• Native AOT publish plus VLC export/import smoke passed
• repo-local VLC 4 lifecycle integration passed
• OpenVINO GPU runtime check stayed below the 0.75 real-time-factor target after warm-up