fix(operations): disabling the halacha drain now stops a running process immediately

The /operations "disabled" toggle only wrote drain_controls.disabled, which the
drain checks at STARTUP — so a drain already mid-run kept going until the queue
emptied or the night window closed. Disabling did not stop a running drain.

Three layers, immediate + backstops:
- web/app.py operations_drain_toggle: on disable, also stop the running process
  immediately via the host pm2 bridge (_ops_pm2_control). Best-effort — a bridge
  failure doesn't fail the toggle.
- halacha_drain_supervisor.py: each tick now reads the disabled flag (added to
  db_snapshot) and, when set, stops the drain and never re-triggers it —
  regardless of burst/window. Backstop if the UI path failed (≤ one tick).
- drain_halacha_queue.py: re-check is_drain_disabled at the top of every round,
  so a drain disabled mid-run halts at the next round boundary. Per-chunk
  checkpoints mean the in-flight case loses nothing.

SCRIPTS.md updated for both drain and supervisor.

Invariants: G1 (fix at source — the disable control honoured along every path,
not just at startup); G2 (no parallel control path — same drain_controls flag).

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

scripts/drain_halacha_queue.py

@@ -62,6 +62,14 @@ async def main():
     empty_rounds = 0
     rnd = 0
     while empty_rounds < 2:
+        # Re-check the /operations kill-switch each round so a drain disabled
+        # mid-run halts at the next round boundary (not only at startup). The UI
+        # toggle + supervisor stop the process outright; this is the in-process
+        # backstop. Per-chunk checkpoints mean the current case loses nothing.
+        if await db.is_drain_disabled("legal-halacha-drain"):
+            print(f"===STOP=== disabled via /operations mid-run — halting "
+                  f"({total} cases this run; resumes when re-enabled)", flush=True)
+            break
         if not _in_window():
             print(f"===STOP=== drain window closed ({_WINDOW_END:02d}:00) — "
                   f"{total} cases this run; rest resumes next night", flush=True)