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.

deploy/mavend.json

@@ -26,6 +26,11 @@
     "severity_ceiling": 2
   },
 
+  "pattern_proposals": {
+    "notify": false,
+    "cooldown": "24h"
+  },
+
   "nexus":  { "url": "http://nexus:9740" },
   "praxis": { "url": "http://praxis:8989" },
   "hexis":  { "url": "http://hexis:9741" },