- Add storage.shares table with indexes on token, (item_id, item_type), created_by
- Create SharePgRepository with indexed SQL queries and window-function pagination
- Rewire DI to inject SharePgRepository with PgPool instead of config
- Delete legacy share_fs_repository.rs (295 lines of JSON file I/O)
- Remove dead module declaration from repositories/mod.rs
Eliminates O(n) full-file JSON reads/writes, TOCTOU races, and crash
corruption risk. All share operations now use indexed PG queries.