feat(5.20): US-013 retragere accounts.rar_creds_enc -> per-env + DROP cu garda

Toate citirile pe coloana legacy accounts.rar_creds_enc mutate pe sloturile
per-env (rar_creds_test_enc/rar_creds_prod_enc): worker fallback+keepalive,
are_creds (web) si are_creds_rar (integrare, +are_creds_test/_prod), write-back
API la reactivare, purjare la stergere cont, _get_acasa_context/_fetch_cont_env_state.

Contract API (aditiv): POST /v1/conturi/rar-creds primeste rar_target optional
(test/prod), scrie in slotul corect + activeaza mediul; DELETE primeste ?env
(sterge un slot sau ambele). Documentat in docs/api-rar-contract.md.

DROP cu garda in db.py (schema.sql fara coloana pe DB fresh):
- 6a: eliminat ADD COLUMN rar_creds_enc (fara ping-pong re-ADD dupa DROP)
- 6b: try/except fail-safe (nu crapa boot-ul) + garda sqlite_version >= 3.35
- 6c: re-backfill old->new imediat inainte de assert (ancora globala)
- garda orfane: DROP anulat daca vreun creds legacy nu a aterizat in slot per-env
- backup criptat accounts_rar_creds_enc_backup inainte de DROP
- 6d: verificare prin PRAGMA table_info (NU grep — submissions are aceeasi coloana)
Garda one-way, idempotenta la boot repetat (verificat). submissions.rar_creds_enc
ramane neatinsa.

tests/test_retragere_creds_enc.py: niciun read pe coloana veche, conturi rar-creds
env-aware, are_creds per-env, DROP blocat de garda la lipsa copiere. 9 teste
existente actualizate pe sloturi per-env.

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

tests/test_integrare_api.py

@@ -61,13 +61,16 @@ def _creeaza_cheie(monkeypatch) -> str:
 
 
 def _seteaza_rar_creds(monkeypatch=None) -> None:
-    """Seteaza rar_creds_enc pe contul id=1."""
+    """Seteaza creds RAR pe contul id=1 (slotul per-env, US-013)."""
     from app.db import get_connection
     from app.crypto import encrypt_creds
     conn = get_connection()
     try:
         enc = encrypt_creds({"email": "test@rar.ro", "password": "secret"})
-        conn.execute("UPDATE accounts SET rar_creds_enc=? WHERE id=1", (enc,))
+        # US-013: scrie in slotul per-env (test = ancora globala in teste)
+        conn.execute(
+            "UPDATE accounts SET rar_creds_test_enc=?, rar_test_enabled=1 WHERE id=1", (enc,)
+        )
         conn.commit()
     finally:
         conn.close()