feat(cases): Evidence selection + disclosure foundation

Parent: #145

Scope

Implement decomposition item 2: Data/Add-to-case, Alerts/Tracks entry points, Case evidence browser, attachment selection, timeline/map, changed/deleted/unsynced evidence handling, and disclosure transforms.

Dependencies

Blocked by #268 (Cases foundation).

Required invariants

• Evidence remains linked to underlying CoMapeo observations/alerts/tracks/attachments with provenance.
• Model changed/deleted/unavailable/unsynced evidence explicitly.
• Disclosure is per report/agency: identities, people, Exact/Area only/Omit location, individual media, and other sensitive fields.
• Hidden location cannot leak through payloads, maps, logs, activity, or shared-media metadata.
• Shared photo/audio uses metadata-scrubbed derivatives with original→derivative hashes; raw originals remain source/local only and never reporting R2.
• No AI upload/transcription in this scope; local/offline remains first class.
• TDD and all AGENTS.md gates.

Acceptance

Implement all #145 requirements attributable to decomposition item 2 with focused tests and relevant desktop/mobile E2E; complete the full AGENTS.md verification matrix before PR readiness.

Start by reading parent issue #145, blocker #268, and the repository's AGENTS.md files to understand the decomposition and verification gates. Map the listed evidence, disclosure, provenance, and offline requirements across the existing cases and data entry points, then add focused tests plus relevant desktop/mobile E2E; done means the full AGENTS.md verification matrix passes and all stated acceptance requirements are covered.