feat: add Scheduler provider + multi-provider UX fixes

Scheduler provider:
- Virtual provider (no external service) that emits SCHEDULED_MESSAGE
  events on user-defined intervals or cron expressions
- Custom variables stored in tracker filters, flattened into template context
- fire_count persists across triggers via tracker state
- APScheduler CronTrigger support for cron-mode schedules
- Default templates (EN+RU), seeded on startup

Multi-provider UX fixes:
- Tracking config hides Immich-specific sections (periodic, scheduled,
  memory, asset display) for non-Immich providers
- Command config driven by provider capabilities — hides commands/settings
  for providers without bot commands
- Template config hides empty "Scheduled Messages" group
- Test menu on tracker targets is provider-aware (Immich shows all 4 test
  types, others show only basic)
- Removed redundant Test button from tracker card
- System-owned tracking configs (user_id=0) seeded for Gitea + Scheduler
- Fixed ownership checks to allow system configs in tracker-target links
- Capabilities cache shared across template-configs and command-configs
- Command tracker bot selector uses EntitySelect instead of raw select
- Sample context includes Gitea + Scheduler variables for template preview

frontend/src/routes/notification-trackers/TrackerForm.svelte

@@ -14,6 +14,7 @@
 			collection_ids: string[];
 			scan_interval: number;
 			batch_duration: number;
+			filters: Record<string, any>;
 		};
 		providerItems: { value: number; label: string; icon: string; desc: string }[];
 		collections: any[];
@@ -22,6 +23,7 @@
 		submitting: boolean;
 		linkCheckLoading: boolean;
 		error: string;
+		providerType: string;
 		onsave: (e: SubmitEvent) => void;
 		ontoggleCollection: (collectionId: string) => void;
 		formatDate: (dateStr: string) => string;
@@ -36,10 +38,39 @@
 		submitting,
 		linkCheckLoading,
 		error,
+		providerType = '',
 		onsave,
 		ontoggleCollection,
 		formatDate,
 	}: Props = $props();
+
+	let isScheduler = $derived(providerType === 'scheduler');
+
+	// Custom variable management for scheduler
+	function addVariable() {
+		const vars = { ...(form.filters.custom_variables || {}) };
+		const key = `var_${Object.keys(vars).length + 1}`;
+		vars[key] = '';
+		form.filters = { ...form.filters, custom_variables: vars };
+	}
+	function removeVariable(key: string) {
+		const vars = { ...(form.filters.custom_variables || {}) };
+		delete vars[key];
+		form.filters = { ...form.filters, custom_variables: vars };
+	}
+	function updateVariableKey(oldKey: string, newKey: string) {
+		if (!newKey || newKey === oldKey) return;
+		const vars = { ...(form.filters.custom_variables || {}) };
+		const val = vars[oldKey] ?? '';
+		delete vars[oldKey];
+		vars[newKey] = val;
+		form.filters = { ...form.filters, custom_variables: vars };
+	}
+	function updateVariableValue(key: string, value: string) {
+		const vars = { ...(form.filters.custom_variables || {}) };
+		vars[key] = value;
+		form.filters = { ...form.filters, custom_variables: vars };
+	}
 </script>
 
 <div in:slide={{ duration: 200 }}>
@@ -57,7 +88,7 @@
 			<label class="block text-sm font-medium mb-1">{t('notificationTracker.server')}</label>
 			<EntitySelect items={providerItems} bind:value={form.provider_id} placeholder={t('notificationTracker.selectServer')} />
 		</div>
-		{#if collections.length > 0}
+		{#if !isScheduler && collections.length > 0}
 			<div>
 				<label class="block text-sm font-medium mb-1">{t('notificationTracker.albums')} ({collections.length})</label>
 				<input type="text" bind:value={collectionFilter} placeholder="Filter..."
@@ -77,6 +108,59 @@
 				</div>
 			</div>
 		{/if}
+
+		{#if isScheduler}
+			<!-- Schedule type -->
+			<fieldset class="border border-[var(--color-border)] rounded-md p-3">
+				<legend class="text-sm font-medium px-1">{t('notificationTracker.scheduleType')}</legend>
+				<div class="flex gap-4 mt-1">
+					<label class="flex items-center gap-2 text-sm">
+						<input type="radio" name="schedule_type" value="interval"
+							checked={!form.filters.schedule_type || form.filters.schedule_type === 'interval'}
+							onchange={() => form.filters = { ...form.filters, schedule_type: 'interval' }} />
+						{t('notificationTracker.intervalMode')}
+					</label>
+					<label class="flex items-center gap-2 text-sm">
+						<input type="radio" name="schedule_type" value="cron"
+							checked={form.filters.schedule_type === 'cron'}
+							onchange={() => form.filters = { ...form.filters, schedule_type: 'cron' }} />
+						{t('notificationTracker.cronMode')}
+					</label>
+				</div>
+				{#if form.filters.schedule_type === 'cron'}
+					<div class="mt-3">
+						<label for="trk-cron" class="block text-xs mb-1">{t('notificationTracker.cronExpression')}</label>
+						<input id="trk-cron" value={form.filters.cron_expression || ''}
+							oninput={(e) => form.filters = { ...form.filters, cron_expression: (e.target as HTMLInputElement).value }}
+							placeholder="0 9 * * 1-5" class="w-full px-3 py-2 border border-[var(--color-border)] rounded-md text-sm bg-[var(--color-background)] font-mono" />
+						<p class="text-xs text-[var(--color-muted-foreground)] mt-1">{t('notificationTracker.cronHint')}</p>
+					</div>
+				{:else}
+					<div class="mt-3">
+						<label for="trk-interval" class="block text-xs mb-1">{t('notificationTracker.scanInterval')}<Hint text={t('hints.scanInterval')} /></label>
+						<input id="trk-interval" type="number" bind:value={form.scan_interval} min="60" max="86400" class="w-full px-3 py-2 border border-[var(--color-border)] rounded-md text-sm bg-[var(--color-background)]" />
+					</div>
+				{/if}
+			</fieldset>
+
+			<!-- Custom variables -->
+			<fieldset class="border border-[var(--color-border)] rounded-md p-3">
+				<legend class="text-sm font-medium px-1">{t('notificationTracker.customVariables')}</legend>
+				<p class="text-xs text-[var(--color-muted-foreground)] mb-2">{t('notificationTracker.customVariablesHint')}</p>
+				{#each Object.entries(form.filters.custom_variables || {}) as [key, value]}
+					<div class="flex gap-2 mb-2 items-center">
+						<input value={key} onblur={(e) => updateVariableKey(key, (e.target as HTMLInputElement).value)}
+							placeholder="key" class="w-1/3 px-2 py-1.5 border border-[var(--color-border)] rounded-md text-sm bg-[var(--color-background)] font-mono" />
+						<input value={value} oninput={(e) => updateVariableValue(key, (e.target as HTMLInputElement).value)}
+							placeholder="value" class="flex-1 px-2 py-1.5 border border-[var(--color-border)] rounded-md text-sm bg-[var(--color-background)]" />
+						<button type="button" onclick={() => removeVariable(key)}
+							class="text-[var(--color-error-fg)] hover:opacity-70 text-sm px-1">✕</button>
+					</div>
+				{/each}
+				<button type="button" onclick={addVariable}
+					class="text-xs text-[var(--color-primary)] hover:underline mt-1">+ {t('notificationTracker.addVariable')}</button>
+			</fieldset>
+		{:else}
 		<div class="grid grid-cols-2 gap-3">
 			<div>
 				<label for="trk-interval" class="block text-sm font-medium mb-1">{t('notificationTracker.scanInterval')}<Hint text={t('hints.scanInterval')} /></label>
@@ -87,6 +171,7 @@
 				<input id="trk-batch" type="number" bind:value={form.batch_duration} min="0" max="3600" class="w-full px-3 py-2 border border-[var(--color-border)] rounded-md text-sm bg-[var(--color-background)]" />
 			</div>
 		</div>
+		{/if}
 
 		<button type="submit" disabled={submitting || linkCheckLoading} class="px-4 py-2 bg-[var(--color-primary)] text-[var(--color-primary-foreground)] rounded-md text-sm font-medium hover:opacity-90 disabled:opacity-50">
 			{#if linkCheckLoading}{t('notificationTracker.checkingLinks')}{:else}{editing ? t('common.save') : t('notificationTracker.createTracker')}{/if}