fix(fire): remove immediate-severity exemption from grouper + cooldown

Fire events carried _severity_override="immediate" which zeroed the
dispatcher cooldown and skipped the Grouper coalescer. This meant fire
had no rate control in normal live operation. Drain-mode pacer handles
reconnect bursts; this change closes the live-operation gap so fire
obeys the toggle cooldown_seconds like every other family.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

meshai/notifications/pipeline/dispatcher.py

@@ -379,14 +379,13 @@ class Dispatcher:
             return
 
         # ---------- Section 3 — per-toggle cooldown (check only) ----------
-        # Immediate-severity events bypass cooldown entirely — they are
-        # already rate-controlled by source handler change detection.
+        # All severities (including immediate) obey cooldown. Fire rate
+        # control was previously bypassed for immediate; the drain-mode
+        # pacer handles reconnect bursts, and this cooldown handles
+        # normal live operation (≤1 per cooldown window per toggle/key).
         # v0.6-4 (B13 fix): this section only CHECKS the cooldown. Arming
         # it is deferred to Section 6 and happens only after a delivery
         # actually succeeded.
-        if getattr(event, "severity", None) == "immediate":
-            cooldown_s = 0
-        else:
         cooldown_s = int(getattr(tog, "cooldown_seconds", 300) or 0)
         ck = None
         if cooldown_s > 0:

meshai/notifications/pipeline/grouper.py

@@ -100,12 +100,6 @@ class Grouper:
         event with the same group_key. The held event is emitted
         later via tick().
         """
-        # Immediate-severity events bypass the coalescing window entirely
-        # (Phase 2.16.1): they must be delivered without buffering latency.
-        if event.severity == "immediate":
-            self._next(event)
-            return
-
         if not event.group_key:
             self._next(event)
             return