fix(notifications): v0.5.2 -- staleness filter, cooldown, dedup, renderer wiring, hydro family

Spam fix from v0.5.0 oversight:
- Staleness filter (default 600s, configurable per-toggle) drops backlog at dispatcher
  entrance -- solves the "restart wave fires days of old events" problem definitively.
- Per-toggle cooldown_seconds (default 300s) throttles same (category, region) bursts.
- Per-(source, event_id) LRU dedup (10k entries) catches Central re-delivery.
- Renderer wired into _dispatch_toggles; toggle path now produces friendly mesh strings
  with 150-byte UTF-8 hard cap and priority-order segment composition (no mid-char trunc).
- categories.py: stream_flood_warning / stream_high_water moved from weather -> geohazards
  family (canonical toggle name = seismic in VALID_TOGGLES) to match the GUI family tab.

Verified end-to-end: 7200s-old events all dropped (100/0), fresh burst throttles to one
mesh broadcast per cooldown window (1/99), dedup catches duplicate event_ids (1/99).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

meshai/config.py

@@ -535,6 +535,9 @@ class NotificationToggle:
     # severity -> list of channel types (digest|mesh_broadcast|mesh_dm|email|webhook)
     severity_channels: dict = field(default_factory=dict)
     quiet_hours_override: bool = True  # immediate-only quiet-hours bypass
+    # v0.5.2: staleness drop + per-toggle cooldown (Matt's spam fix)
+    freshness_seconds: int = 600   # drop events older than this at dispatcher entrance
+    cooldown_seconds: int = 300    # per (toggle, category, region) throttle window
     # per-channel delivery config (mirrors NotificationRuleConfig channel fields)
     broadcast_channel: Optional[int] = None
     node_ids: list = field(default_factory=list)