fix(activity): runs keep their true outcome and spend, the page reaches every kept row, a closing dialog leaves the server log alone

Backend
- A run's outcome write sits outside the job's own try: a database blip after a run that
  succeeded no longer records it as failed (the row waits for the next start's sweep).
- An interrupted run keeps what it spent (the sweep sums its quota rows, as finish does).
- The Scheduler's ad-hoc row says running while any backfill runs, not only the newest.
- recent_runs reads each job's last runs off its index instead of ranking the whole table.
- An interval change is stored with its audit row in one transaction, then rescheduled.
- One API instance per database is the stated contract (.env.example, jobruns).
- Turning full history on for a channel already complete records no run.
- Migration 0109 round-trips interrupted and ad-hoc runs; the run words' DB CHECKs are
  test-held to the enums; the account filter is one helper for the four activity reads.
- An audit row says how many of its request's log lines are still kept.

Frontend
- An "All" period reaches every row still kept (runs and admin actions outlive 90 days).
- Back/Forward is followed in place by the server log: a closing dialog no longer turns
  Live off; a pivot still opens a fresh log.
- Runs moved over from the audit log read their one-liner in the reader's language.
- Filter choices or accounts that failed to load say so beside the filters, with a retry.
- An old server-log link keeps its account, text and range; a remembered retired page
  opens its tab.
- A request whose lines are gone says so instead of linking to an empty list.
- The log lines and the history rows share one row frame, and the server log one list
  frame with the other tabs; an empty list is announced; each day's quota is readable.

backend/tests/test_channel_backfill.py

@@ -136,6 +136,19 @@ def test_deep_request_starts_the_backfill_as_the_users_run_of_that_channel(
     assert calls == [(ch.id, me.id)]
 
 
+def test_turning_full_history_on_for_a_finished_channel_records_no_run(
+    db, monkeypatch, override_dep
+):
+    """Its whole history is in already: a run would only say "nothing to do", and switching the flag
+    off and on again would otherwise write one such row each time, kept for months."""
+    ch, me = _setup_channel_and_sub(db, email="done@example.com")
+    ch.backfill_done = True
+    db.commit()
+    resp, submitted, calls = _patch_deep_requested(db, monkeypatch, override_dep, me)
+    assert resp.status_code == 200, resp.text
+    assert (submitted, calls) == ([], [])
+
+
 class TestImmediateBackfillGuard:
     """backfill_channel_now coordinates with the paced scheduler through _backfill_in_progress (per-
     channel mutual exclusion, both directions) + _immediate_running (a cap on interactive runs so a