feat: add notification suppression rules (#1525)

* feat: add notification suppression rules

* fix: restore label routing and routing test mocks for suppression

* fix: allow bell mute shortcuts for history-only notification categories

Suppression rule validation used the routable category whitelist, which rejected history-only categories such as update_started that appear in the bell during stack updates.

* feat: expand Mute Rules UX with compose-first entry points and activity badges

* fix: add missing NodeContext mocks for notification suppression tests

docs/reference/settings.mdx

@@ -419,6 +419,32 @@ See [Notification Routing](/features/alerts-notifications#notification-routing)
 
 ---
 
+## Mute Rules
+
+<Note>
+  Creating, editing, and deleting mute rules is admin-only.
+</Note>
+
+**Scope:** Global, admin-only
+
+Create notification suppression rules that mute or drop matching alerts from the bell, external channels, or both. Suppression is evaluated before routing. The masthead publishes **RULES** and **ACTIVE** counts.
+
+| Field | Description |
+|-------|-------------|
+| **Name** | Operator-facing label for the rule. |
+| **Node** | Specific node, or all nodes if left empty. |
+| **Stack patterns** | Stack names to match (multi-select). |
+| **Labels** | Match stacks that carry any selected label. |
+| **Categories** | Notification categories to suppress. |
+| **Severity** | Info, warning, and/or error levels to suppress. |
+| **Apply to** | Bell only, external channels only, or both. |
+| **Expiration** | Forever, 1 hour, 24 hours, or a custom timestamp. |
+| **Enabled** toggle | Disable a rule without deleting it. |
+
+See [Mute Rules](/features/alerts-notifications#mute-rules) for the full walkthrough, compose-first shortcuts, and bell quick-mute.
+
+---
+
 ## Image update checks
 
 **Scope:** Per-node (applies to the currently selected node)