Announce tick-inferred routines, opt-in and rate-limited (#247, #43)

The digestion tick already runs the pattern detector over all recorded
events (67563ed) and writes a proposed_routines row. What was missing is
the other half of #247: a proposal that nobody is at the mic for reaches
nothing but the /routines page, so a pattern noticed at 03:00 is only
seen if he goes looking.

This wires the tick's proposals into the existing care-delivery path
rather than a second channel: sev1 nudge, loop.Gate, dispatcher, same
routing table as an accepted routine. Restraints, since a feature that
speaks unprompted is the easiest way to turn Maven into a nag:

  - off unless configured — the new pattern_proposals block, absent by
    default, and deploy/mavend.json ships notify: false;
  - at most one announcement per tick however many patterns surfaced;
  - at most one per cooldown (24h default) across all pairs;
  - sev1, so quiet hours, away and snooze suppress it;
  - suppressed means dropped, not queued — /routines still has it;
  - once per pair for good, since proposed_routines is
    UNIQUE(action, object) and the row survives dismissal.

The body is pattern.PhraseRoutine's literal Russian, not LLM-worded, so
an inferred routine cannot arrive describing something never observed.

Also raises pattern.MinEvents from 3 to 4 — the interval-quality item on
#43. Two intervals with a ±50% band is a coincidence with a mean, not a
pattern, and now that a scan of all history can announce itself the cost
of a false positive is a permanent dismissal of that pair.

cmd/mavend/tick_test.go

@@ -46,7 +46,7 @@ func newTestTickLoop(t *testing.T, st *store.Store, sink delivery.Sink, digestCf
 		Nudges:    st,
 		Reminders: st,
 	})
-	return newTickLoop(st, g, d, phraser.NewStub(), rules, time.Second, 5*time.Minute, 0, digestCfg, nil, nil)
+	return newTickLoop(st, g, d, phraser.NewStub(), rules, time.Second, 5*time.Minute, 0, digestCfg, nil, nil, nil)
 }
 
 func TestTickFiresRoutineWhenScheduleCrosses(t *testing.T) {
@@ -63,7 +63,7 @@ func TestTickFiresRoutineWhenScheduleCrosses(t *testing.T) {
 	sink := &fakeSink{}
 	d := delivery.NewDispatcher(delivery.Config{Voice: sink, Ntfy: sink, Telegram: sink, Nudges: st, Reminders: st})
 	rs := []routine.Routine{{Name: "morning", Cron: "0 12 * * *", Body: "полдень, время воды", Severity: 1}}
-	tl := newTickLoop(st, g, d, phraser.NewStub(), rules, time.Second, 5*time.Minute, 0, nil, rs, nil)
+	tl := newTickLoop(st, g, d, phraser.NewStub(), rules, time.Second, 5*time.Minute, 0, nil, rs, nil, nil)
 
 	// first tick: seeds, does not fire the routine.
 	tl.tick(ctx, now)