feat: add evidence-backed canonical media indexes

[jamiesun]

Summary

• Define structured observation and artifact schemas with stable IDs, millisecond time ranges, evidence references, producer/version, status, and confidence.
• Add derived artifact registration, evidence-aware FFmpeg scanning, deterministic canonical index synthesis, conflict reporting, scene segments, and filtered queries.
• Extend capability planning with required/optional/if-available levels plus precision and external-processing constraints.
• Update the FilmMap skill, documentation, and roadmap; expand CLI and FFmpeg E2E coverage.

Verification

• make check
• make e2e
• make book
• bash -n install.sh tools/*.sh
• One real DJM clip scan, structured scene/location observations, canonical validation, and millisecond query. The clip's location remains unknown; no external geolocation model was run.

Notes

This PR does not include a release. Homebrew/apt/curl installation and clean-platform release verification remain separate follow-up work.