Investigation: add durable private bookmarks

[matteius]

Summary

• save the current multi-camera investigation window, cursor, primary camera, filters, region, and representative result
• provide a private bookmark workspace for listing, reopening, and revision-safe deletion
• retain private notes server-side without placing them in navigation URLs

Authorization and retention

• every bookmark access re-evaluates current recordings.replay permission across all saved cameras
• bookmarks outside the current camera scope are omitted from lists and blocked on direct access
• bookmarks explicitly report holds_recordings: false and the UI warns that they do not protect media from retention or deletion
• create, update, and delete outcomes are audited
• demo mode exposes an empty read-only workspace

Persistence and API

• adds owner-private, revisioned bookmark tables in migration 0064
• adds list, create, read, metadata update, and delete endpoints under /api/investigation-bookmarks
• stores only a bounded whitelist of navigation-safe filter and result fields

Validation

• full combined C build
• 7 focused database, auth, authorization, audit, and investigation test targets
• 18 frontend suites with 125 tests
• production Vite build

Migration order

#537 has merged and owns migration 0063; this PR follows it with 0064.