feat(import): T1 accounts.rar_creds_enc durabil + worker fallback + gate purjare
- worker: _creds_from_account(conn, account_id) — fallback la accounts.rar_creds_enc
cand submission n-are creds (canal web fara re-pusher, restart worker)
- run(): creds = _creds_for(claimed, settings) OR _creds_from_account(conn, account_id)
- gate purjare (Voce#5): comentariu explicit — sterge DOAR submissions.rar_creds_enc,
NU accounts.rar_creds_enc (inofensiv pt canal web, neatins pt canal API)
- POST /v1/conturi/rar-creds: seteaza creds durabile criptate Fernet per cont
- DELETE /v1/conturi/rar-creds: revenire la modelul efemer Treapta 1
- 7 teste: fallback, restart, coada mixta, endpoint set/delete, gate purjare
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>