feat: default tracker configs, email validation, expandable target links

- Tracker now has default_tracking_config_id and default_template_config_id
  that apply to all linked targets unless overridden per-target
- Dispatch falls back to tracker defaults when per-link configs are null
- Email bot creation validates SMTP connection before saving
- Email notifications sent as HTML (links render properly)
- Linked target items are expandable: collapsed shows config CrossLinks,
  expanded shows config selectors; action buttons always visible
- Fix email bot test button icon (mdiEmailSend → mdiSend)
- Fix target type icons in LinkedTargetsSection for all types
- Provider filter moved above search in sidebar

frontend/src/routes/notification-trackers/+page.svelte

@@ -61,6 +61,7 @@
 	const defaultForm = () => ({
 		name: '', icon: '', provider_id: 0, collection_ids: [] as string[],
 		scan_interval: 60, batch_duration: 0,
+		default_tracking_config_id: 0, default_template_config_id: 0,
 		filters: {} as Record<string, any>,
 	});
 	let form = $state(defaultForm());
@@ -143,6 +144,8 @@
 			name: trk.name, icon: trk.icon || '', provider_id: trk.provider_id,
 			collection_ids: [...(trk.collection_ids || [])],
 			scan_interval: trk.scan_interval, batch_duration: trk.batch_duration ?? 0,
+			default_tracking_config_id: (trk as any).default_tracking_config_id || 0,
+			default_template_config_id: (trk as any).default_template_config_id || 0,
 			filters: trk.filters || {},
 		};
 		previousCollectionIds = [...(trk.collection_ids || [])];
@@ -179,11 +182,16 @@
 	async function doSave() {
 		submitting = true;
 		try {
+			const payload = {
+				...form,
+				default_tracking_config_id: form.default_tracking_config_id || null,
+				default_template_config_id: form.default_template_config_id || null,
+			};
 			if (editing) {
-				await api(`/notification-trackers/${editing}`, { method: 'PUT', body: JSON.stringify(form) });
+				await api(`/notification-trackers/${editing}`, { method: 'PUT', body: JSON.stringify(payload) });
 				snackSuccess(t('snack.trackerUpdated'));
 			} else {
-				await api('/notification-trackers', { method: 'POST', body: JSON.stringify(form) });
+				await api('/notification-trackers', { method: 'POST', body: JSON.stringify(payload) });
 				snackSuccess(t('snack.trackerCreated'));
 			}
 			showForm = false; editing = null; linkWarning = null; await load();
@@ -371,6 +379,8 @@
 		{providerItems}
 		{collections}
 		bind:collectionFilter
+		trackingConfigItems={trackingConfigs.filter(c => !selectedProviderType || c.provider_type === selectedProviderType).map(c => ({ value: c.id, label: c.name, icon: (c as any).icon || 'mdiCog' }))}
+		templateConfigItems={templateConfigs.filter(c => !selectedProviderType || c.provider_type === selectedProviderType).map(c => ({ value: c.id, label: c.name, icon: (c as any).icon || 'mdiFileDocumentEdit' }))}
 		{editing}
 		{submitting}
 		{linkCheckLoading}
@@ -406,7 +416,7 @@
 	</Card>
 {:else if !showForm}
 	<div class="space-y-3 stagger-children">
-		{#each notificationTrackers as tracker}
+		{#each notificationTrackers as tracker (tracker.id)}
 			<Card hover entityId={tracker.id}>
 				<div class="flex items-center justify-between">
 					<div>