feat(5.20): US-004/005/006/009 ingestie+API+worker+import pe mediu RAR

US-004: rezolva_rar_env (cerere>default cont>ancora globala) + MediuIndisponibil
+ cod RAR_MEDIU_INDISPONIBIL.
US-005: camp rar_env pe POST /v1/prezentari + /valideaza (Literal), echo in
SubmissionResult/ValidareResult/GET, build_key + INSERT env-aware.
US-006: AccountSessions re-cheiat (account_id, rar_env); RarClient base_url per
env; creds din slotul env; purge + recover_orphans scoped pe env (E1/1a, 1b/E6);
claim_one propaga rar_env (1c/E8); keepalive pe ancora globala (M2).
US-009: selector mediu la import (>=2 medii), eticheta la 1, banner la 0; commit
seteaza rar_env pe submissions.

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

tests/test_worker_keepalive_rar.py

@@ -42,10 +42,10 @@ class _FakeSessions:
         self.invalidated: list[int] = []
         self.tokens: list[int] = []
 
-    def invalidate(self, account_id: int) -> None:
+    def invalidate(self, account_id: int, rar_env=None) -> None:
         self.invalidated.append(account_id)
 
-    def get_token(self, conn, account_id: int, creds) -> str | None:
+    def get_token(self, conn, account_id: int, creds, rar_env="test") -> str | None:
         self.tokens.append(account_id)
         if self._fail:
             raise RuntimeError("RAR jos")