feat: provider-strict configs, slot-based templates, broadcast targets, email bots, command templates

Major architectural improvements:
- Provider-type enforcement: configs validated against provider type at assignment
- TemplateConfig migrated to slot-based pattern (TemplateSlot child table)
- Broadcast targets: TargetReceiver child table for multi-receiver dispatch
- EmailBot: first-class email sender entity with SMTP config, test connection
- CommandTemplateConfig: generic slot-based command response templates
- Provider capability registry: dynamic slot/event/command definitions per provider
- CommandTracker play/pause button matches NotificationTracker style

frontend/src/routes/+layout.svelte

@@ -46,6 +46,7 @@
 		{ href: '/targets', key: 'nav.targets', icon: 'mdiTarget' },
 		{ href: '/command-trackers', key: 'nav.commandTrackers', icon: 'mdiConsoleLine' },
 		{ href: '/command-configs', key: 'nav.commandConfigs', icon: 'mdiCog' },
+		{ href: '/command-template-configs', key: 'nav.cmdTemplateConfigs', icon: 'mdiCodeBracesBox' },
 	];
 	const navItems = $derived(auth.isAdmin
 		? [...baseNavItems, { href: '/users', key: 'nav.users', icon: 'mdiAccountGroup' }, { href: '/settings', key: 'nav.settings', icon: 'mdiCogOutline' }]