Reject cross-tenant skill grant and revoke operations before grant rows or skill visibility can be changed. Clean legacy invalid grant rows in PostgreSQL and SQLite migrations, hide owner IDs from skill API/UI responses, and cover the tenant-isolation cases with PG and SQLite regression tests.
Upload handler previously archived skills immediately when deps were
missing. Now calls InstallDeps() first (owner/master tenant only) and
falls back to archive on failure.
Changes:
- Auto-install missing deps during skill upload (same flow as seeder)
- Atomic DB persist: deps state written with CreateSkillManaged in one call
- Per-slug upload mutex prevents concurrent race conditions
- Frontend: warning state (amber triangle) instead of throwing error
- Non-cancellable context for DB write after dep install
- SQLite StoreMissingDeps now works for custom skills (not just system)
- Comprehensive unit + integration tests
Closes#468
