feat: channel audit logging, name cleaning, message formatting, and dashboard UI

- Add audit log entries for channel create, update, rotate_config, delete
- Clean channel names on create/update (trim, lowercase, spaces → hyphens,
  SafeName validation)
- Format chat notifications with full event details (resource, actor, team,
  timestamp) instead of one-liners
- Fix Discord split-line embeds by setting splitLines=No on shoutrrr URL
- Add channels dashboard page and sidebar navigation

frontend/src/lib/components/Sidebar.svelte

@@ -22,7 +22,8 @@
 		IconAudit,
 		IconServer,
 		IconShield,
-		IconMetrics
+		IconMetrics,
+		IconBroadcast
 	} from './icons';
 
 	let { collapsed = $bindable(false) }: { collapsed: boolean } = $props();
@@ -58,6 +59,7 @@
 
 	let managementItems = $derived<NavItem[]>([
 		{ label: 'Keys', icon: IconKey, href: '/dashboard/keys' },
+		{ label: 'Channels', icon: IconBroadcast, href: '/dashboard/channels' },
 		{ label: 'Team', icon: IconMembers, href: '/dashboard/team' },
 		{ label: 'Audit Logs', icon: IconAudit, href: '/dashboard/audit' },
 		...(currentTeamIsByoc