api(encrypted): encrypted-blob and withheld-paths routes skip the quarantine gate

[PierrunoYT]

authorize_repo_read (crates/gitlawb-node/src/api/mod.rs:54-56) drops a quarantined repo before the visibility gate, so a quarantined mirror is hidden from every reader as if it did not exist. The three encrypted-blob handlers (api/encrypted.rs:21-31, 48-58, 84-93) and withheld_paths (api/visibility.rs:213-229) hand-roll the gate with get_repo + visibility_check and never call is_repo_quarantined.

Impact: a quarantined mirror's OID/CID index, and the full ciphertext of every withheld blob via GET .../encrypted-blob/{oid}, are still served, while clone, /ipfs/{cid} and every authorize_repo_read route return 404.

Repro: GET /api/v1/repos/{owner}/{repo}/encrypted-blobs against a quarantined mirror returns 200 with data.

Fix: route these handlers through authorize_repo_read, or add the quarantine check to the hand-rolled gate. Per AGENTS.md, add deny-path tests proving the quarantined repo now 404s on each.

Found in the Oct 2 2026 audit (A2) at bfc44f9.

[beardthelion]

This defect is already fixed in open PR #276, which routes the encrypted-blob handlers and withheld_paths through authorize_repo_read and covers the deny path with a test. Linking so this issue tracks it through merge.