feat(config): job intervals live in sysconfig, every setting says when it applies, the unread SponsorBlock default goes

An interval override was a row of its own table beside the one store every other admin knob uses; it
is now the `job_interval_<job>` sysconfig key (migration 0110 copies them over and drops the table).
The Scheduler page stays its one editor: the Configuration page and the setup wizard neither list nor
write those keys, since a write there would skip the reschedule.

Each ConfigSpec now states `applies` (required, no default). Every key is `live`, held by a scan that
finds no read at import time; a `restart` key is refused until the page can say so. A second scan
requires a reader for every key on the Configuration page — `sponsorblock_default` had none since it
was added, so it leaves the registry, the translations and the store.

backend/tests/test_scheduler.py

@@ -12,7 +12,7 @@ from datetime import datetime, timedelta, timezone
 import pytest
 from sqlalchemy import select
 
-from app import jobruns, logs, logsink, quota, scheduler, state
+from app import jobruns, logs, logsink, quota, scheduler, state, sysconfig
 from app.models import AuditLog, Channel, JobRun, Notification, QuotaEvent
 from app.runstatus import RunStatus, RunTrigger
 
@@ -411,3 +411,54 @@ def test_startup_closes_what_the_previous_process_left_running(db, monkeypatch):
     scheduler.shutdown_scheduler()
     (run,) = _runs(db, "plex_sync")
     assert run.status == "interrupted"
+
+
+def test_every_job_has_an_interval_and_every_interval_a_job():
+    assert set(scheduler.JOB_FUNCS) == set(scheduler.JOB_INTERVALS)
+
+
+def test_a_stored_interval_is_what_the_job_starts_with(db, monkeypatch):
+    sysconfig.set_value(db, "job_interval_rss_poll", 25)
+    db.commit()
+    monkeypatch.setattr(scheduler.settings, "scheduler_enabled", True)
+    scheduler.start_scheduler()
+    try:
+        sched = scheduler._scheduler
+        assert sched is not None
+        assert sched.get_job("rss_poll").trigger.interval == timedelta(minutes=25)
+        default = scheduler.JOB_INTERVALS["enrich"]
+        assert sched.get_job("enrich").trigger.interval == timedelta(minutes=default)
+    finally:
+        scheduler.shutdown_scheduler()
+
+
+def test_an_interval_set_on_the_scheduler_page_is_stored_and_reschedules_the_job(
+    db, make_user, as_user, live_scheduler
+):
+    live_scheduler.add_job(lambda: None, "interval", minutes=10, id="backfill")
+    admin = as_user(make_user(role="admin"))
+    r = admin.patch("/api/admin/scheduler/jobs/backfill", json={"interval_minutes": 45})
+    assert r.status_code == 200, r.text
+    assert live_scheduler.get_job("backfill").trigger.interval == timedelta(minutes=45)
+    db.expire_all()
+    assert sysconfig.get_int(db, "job_interval_backfill") == 45
+    assert scheduler.load_intervals(db)["backfill"] == 45
+    # The Configuration page neither lists an interval nor writes one past the reschedule.
+    assert (
+        admin.patch("/api/admin/config/job_interval_backfill", json={"value": 5}).status_code == 404
+    )
+    assert admin.delete("/api/admin/config/job_interval_backfill").status_code == 404
+    assert "scheduler" not in admin.get("/api/admin/config").json()["groups"]
+    db.expire_all()
+    assert sysconfig.get_int(db, "job_interval_backfill") == 45
+
+
+def test_the_setup_wizard_does_not_write_an_interval(db):
+    from fastapi import HTTPException
+
+    from app.routes.setup import setup_config
+
+    with pytest.raises(HTTPException) as refused:
+        setup_config({"job_interval_rss_poll": 5}, db)
+    assert refused.value.status_code == 400
+    assert setup_config({"quota_daily_budget": 5000}, db)["saved"] == ["quota_daily_budget"]