#125 Add direct file sharing between DIDs

Phase 2: Sharing. Resolve a DID to its public key via DID document, wrap a document's content key to the recipient's pubkey, create a grant record. Also revocation (delete grant) and listing grants. The inbox command (list grants where you're the recipient) may need an AppView for cross-PDS discovery — fine to defer that part or limit to same-PDS queries initially.

Phase 2 status update (2026-03-01):

• #11 closed: DID resolution + public key extraction
• #12 closed: share command (grant creation)
• #13 closed: revoke command (grant deletion)
• #14 closed: shared command (list outgoing grants) + extracted generic list_collection pagination
• #15 open: inbox command — blocked on AppView (see #15 comments for full rationale)

The --grant flag on download is permanent (zero-trust mode), not temporary as originally noted. Even after inbox/AppView exists, --grant provides explicit grant selection without relying on discovery.

Closing #10 as the remaining subissue (#15) is blocked on Phase 4 infrastructure (AppView). All client-side sharing operations are complete.