feat(5.19): auto-send toggle per cont + tinere manuala randuri (held)

Comutator accounts.auto_send_enabled per cont: Auto OFF (default) tine randurile
la ingestie (submissions.held=1), worker-ul (claim_one AND held=0) le sare pana la
eliberare umana (per rand/bulk/auto-release OFF->ON). Snapshot held prin chokepoint
unic held_for_account pe toate caile de ingestie (API, import, reresolve, reactivare).

- schema/migrare: coloana held + index partial idx_submissions_held; auto_send_enabled
- API: echo onest held+motiv (US-010), ruta /prezentari/{id}/trimite-acum
- web: toggle header, modal confirmare tipata, buton Trimite per rand + Trimite toate,
  banner coada tinuta imbatranita (L.142), contor "In asteptare (manual)"
- worker: expire_held (US-008, inchide gaura retentie PII), metrics held gauges
- ops: tools/carantina_held + runbook rollback (R4)

Nota review (/code-review high): re-snapshot held lipseste pe caile repune/corectie
(requeue_submission, post_corectie, bulk-fix) — de aliniat separat cu create_prezentari.

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

app/main.py

@@ -177,9 +177,21 @@ def metrics() -> str:
     conn = get_connection()
     try:
         rows = conn.execute("SELECT status, COUNT(*) AS n FROM submissions GROUP BY status").fetchall()
+        # Coada tinuta (PRD 5.19 US-007): observabilitate ops pt. default Auto OFF.
+        # Gauge-uri DERIVATE (zero stare noua): total randuri tinute + varsta celui
+        # mai vechi (din created_at), scoped global. Semnaleaza esecul silentios
+        # cand prezentari raman nedeclarate tacit (risc L.142).
+        held = conn.execute(
+            "SELECT COUNT(*) AS n, "
+            "COALESCE(MAX(strftime('%s','now') - strftime('%s', created_at)), 0) AS oldest "
+            "FROM submissions WHERE status='queued' AND held=1"
+        ).fetchone()
     finally:
         conn.close()
     lines = ["# submissions pe status"]
     for r in rows:
         lines.append(f'autopass_submissions{{status="{r["status"]}"}} {r["n"]}')
+    # randuri tinute (queued AND held=1)
+    lines.append(f'autopass_held_submissions {held["n"]}')
+    lines.append(f'autopass_held_oldest_age_seconds {held["oldest"]}')
     return "\n".join(lines) + "\n"