feat: add multimodal search and granular performance diagnostics

tools/media-runtime/README.md

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+# Standalone media decoder tools
+
+The desktop distribution must include FFmpeg and FFprobe alongside its Google
+worker. End users should not install tools or configure paths. Development and
+release preparation use:
+
+```sh
+python tools/media-runtime/provision.py --stage
+python -m unittest discover -s tools/media-runtime -p 'test_*.py'
+```
+
+The manifest pins a dated BtbN release, exact archive size, and published SHA-256.
+Provisioning checks the cache or downloads/verifies the archive, extracts only the
+two standalone decoder executables and notices, and stages them under the native
+resources directory. Executables and archives are ignored by Git. No global
+installation occurs. Movie/audio decoding runs in bounded subprocesses.
+
+Windows x86-64/ARM64 and Linux x86-64/ARM64 have pinned artifacts. Only Windows
+x86-64 has been executed here. A vetted macOS decoder build/staging path remains
+a release gate; generic media code can accept native tools through explicit paths.
+The selected build is FFmpeg 9.0.2 with LGPL configuration. Keep original notices
+and corresponding source/build provenance with distribution; installer licensing
+and all-platform execution are still open production gates.
+
+Source/build provenance:
+- https://github.com/BtbN/FFmpeg-Builds/releases/tag/autobuild-2026-10-12-13-12
+- https://github.com/BtbN/FFmpeg-Builds
+- https://ffmpeg.org/legal.html
+
+FFmpeg capabilities vary by build. An unsupported or corrupt file must report an
+error while remaining filename-searchable; it must never freeze search or be
+silently reported as fully indexed.