Harden conversion lifecycle and add media integration tests

[ixiehao]

Summary

• Drain ffprobe output while it runs, isolate progress by conversion attempt, and keep cancellation from publishing a partial result.
• Preserve explicit software/HEVC encoder choices when trimming, cropping, or rotating. Retry only recoverable transient failures.
• Harden Smart Enhance reader/writer/audio/VideoToolbox cancellation and timeout lifecycles.
• Reuse dependency tool checks during queue edits; a manual refresh performs a fresh check.
• Add generated-media integration tests and run swift test in CI after installing FFmpeg.

Verification

• swift test: 10 passed, 0 failed. Includes real native enhancement on macOS 27.0.1, plus conversion, retry, trim/crop/rotation, and >64 KB ffprobe output.
• ./Scripts/run-media-regression.sh: 28 checks passed.
• ./Scripts/validate-localizations.sh: passed.
• swift build -c release: passed.
• Isolated .app build, plist check, code signature structure, and three language resources: passed.

The macOS 27 hardware enhancement test skips on older/unsupported CI Macs; ordinary converter tests still run. Real user media, long videos, and network volumes remain manual release-matrix items.