feat(media): add ffprobe inspection

[TristinWen]

Summary

• add safe, timeout-bounded ffprobe execution without shell interpolation
• parse container, exact duration, video/audio/subtitle streams, codecs, bitrate, frame rate, time base, rotation, color, audio layout, language, and creation metadata
• expose semanticvideo inspect with pretty/compact JSON, output files, executable selection, and timeout controls
• add fixture-driven parser tests, a real synthetic-video CLI integration test, user documentation, and ADR 0006

Motivation

Milestone 2 turns the schema foundation into the first real-video capability. Applications can now obtain validated, reusable technical metadata without an AI provider while keeping subprocess execution separate from deterministic JSON parsing.

Compatibility

• adds optional bitrate fields to media and video/audio stream schemas
• widens rotation_degrees from four right-angle literals to any normalized display-matrix angle
• retains schema version 0.1.0 because existing manifests remain valid
• does not add shot detection or semantic scene understanding

Validation

• ruff check .
• ruff format --check .
• mypy src tests in strict mode
• 57 tests passed with 96.48% coverage
• real FFmpeg 8.1 integration generated a 0.4-second MP4 and validated both inspect_media and semanticvideo inspect --compact
• wheel and source distribution built successfully