Add consent-gated media exchange library

docs/database.md

@@ -14,6 +14,8 @@ The application uses one `better-sqlite3` database, normally `data/reddit-bot.db
 - `reddit_conversations`: account-scoped cached Matrix conversation payloads.
 - `reddit_account_sync_state`: account-scoped sync cursor, full/delta timestamps, and invitation cooldown.
 - `reddit_media`: account-scoped private-media metadata and relative file path.
+- `media_library_assets`: process-global operator-owned image metadata, overlapping anatomy tags, SFW/NSFW classification, consent time, enablement, dimensions, hash, and private relative path.
+- `media_library_sends`: account/conversation/inbound-event reservation and confirmed/failed Matrix delivery audit for a shared library asset.
 
 The special legacy-unassigned account exists only to preserve rows created before account ownership was introduced. New runtime data must use a verified account ID.
 
@@ -50,6 +52,8 @@ The special legacy-unassigned account exists only to preserve rows created befor
 5. Conversation policy is snapshotted in state JSON when automation starts for that conversation.
 6. Secrets and the database path are not stored in `app_config`.
 7. Private media paths in SQLite are relative to the persistent data root; HTTP access remains authenticated.
+8. Received `reddit_media` and operator `media_library_assets` are separate ownership domains; no automatic copy or promotion exists.
+9. A library image content hash has at most one reservation per account conversation, even if the same file is later re-uploaded under a new asset ID; an inbound request also has at most one selected asset. Failed or uncertain attempts remain reserved to prevent duplicates.
 
 ## Repository map