feat(creds): livrare creds per-cerere la worker (criptat efemer + sesiuni per-cont)

Plan sect.5: parola RAR vine per-cerere, stocata CRIPTATA in submission pana la
primul login reusit pe cont, apoi stearsa; JWT 30h acopera restul.

- app/crypto.py: Fernet, cheie din AUTOPASS_creds_key (nesetata -> efemera la
  runtime, creds nu supravietuiesc restartului). encrypt/decrypt_creds.
- schema + migrare: submissions.rar_creds_enc (creds criptate).
- ingestie: cripteaza rar_credentials, le lipeste de fiecare submission nou.
  Niciodata in clar in DB.
- worker: AccountSessions (login per-cont cu creds decriptate, cache JWT in
  memorie, sterge creds-urile contului dupa primul login + refresh nomenclator).
  401 creds gresite -> error fara retry; token expirat -> invalidare + requeue;
  fara creds (restart) -> requeue "indisponibile" (ROAAUTO re-trimite).
  claim_one intoarce account_id + creds_enc; recover_orphans filtrabil pe cont.
- requirements: cryptography==46.0.5.

Nota: refresh nomenclator e acum lazy la primul login per-cont (nu la pornire);
seed-ul fallback acopera editorul offline.

10 teste noi (tests/test_creds_delivery.py). 95 pass total.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/db.py

@@ -46,6 +46,8 @@ def _migrate(conn: sqlite3.Connection) -> None:
     cols = {r["name"] for r in conn.execute("PRAGMA table_info(submissions)").fetchall()}
     if "next_attempt_at" not in cols:
         conn.execute("ALTER TABLE submissions ADD COLUMN next_attempt_at TEXT")
+    if "rar_creds_enc" not in cols:
+        conn.execute("ALTER TABLE submissions ADD COLUMN rar_creds_enc TEXT")
 
 
 def _now_iso() -> str: