refactor: comprehensive consistency review — UI/UX, code quality, functional parity

Fix 19 issues across 3 priority tiers found during full-codebase review:

CRITICAL:
- Fix undefined --color-secondary CSS variable causing invisible UI elements
- Fix Google Photos command templates using nonexistent asset.originalFileName
- Fix scheduler template variable docs (tracker_name → schedule_name)
- Add missing admin guard on notification template update endpoint

HIGH:
- Fix 5 hardcoded English strings missing i18n (MultiEntitySelect, actions,
  settings, TelegramBotTab, users)
- Replace 17 raw <button> elements with shared <Button> component
- Replace 5 raw error divs with shared <ErrorBanner> component
- Refactor webhook handler duplication into shared _dispatch_webhook_event()
- Add 30+ provider-specific fields to TrackingConfig TypeScript type
- Add default TrackingConfig seeds for immich and google_photos
- Add provider-specific command variable docs (Gitea, Planka, NUT, GP, Webhook)

MEDIUM:
- Replace hardcoded hex colors and Tailwind classes with CSS variable tokens
- Remove dead code (unused imports, orphaned check_notification_tracker)
- Fix Svelte 5 patterns ($state for _prevProviderId, remove unnecessary as any)
- Fix inconsistent POST response shape (targets now returns full response)
- Fix Google Photos template dead asset.year branches, clarify album_url docs

frontend/src/routes/actions/+page.svelte

@@ -20,6 +20,8 @@
 	import { providerDefaultIcon } from '$lib/grid-items';
 	import RuleEditor from './RuleEditor.svelte';
 	import ExecutionHistory from './ExecutionHistory.svelte';
+	import ErrorBanner from '$lib/components/ErrorBanner.svelte';
+	import Button from '$lib/components/Button.svelte';
 	import type { Action, ActionRule } from '$lib/types';
 
 	let allActions = $derived(actionsCache.items);
@@ -162,18 +164,17 @@
 	}
 
 	function statusColor(status: string): string {
-		if (status === 'success') return '#059669';
-		if (status === 'partial') return '#f59e0b';
-		if (status === 'failed') return '#ef4444';
+		if (status === 'success') return 'var(--color-success-fg)';
+		if (status === 'partial') return 'var(--color-warning-fg)';
+		if (status === 'failed') return 'var(--color-error-fg)';
 		return 'var(--color-muted-foreground)';
 	}
 </script>
 
 <PageHeader title={t('actions.title')} description={t('actions.description')}>
-	<button onclick={() => { showForm ? (showForm = false, editing = null) : openNew(); }}
-		class="px-3 py-1.5 bg-[var(--color-primary)] text-[var(--color-primary-foreground)] rounded-md text-sm font-medium hover:opacity-90">
+	<Button size="sm" onclick={() => { showForm ? (showForm = false, editing = null) : openNew(); }}>
 		{showForm ? t('common.cancel') : t('actions.addAction')}
-	</button>
+	</Button>
 </PageHeader>
 
 {#if !loaded}
@@ -192,9 +193,7 @@
 {#if showForm}
 	<div in:slide={{ duration: 200 }}>
 	<Card class="mb-6">
-		{#if error}
-			<div class="bg-[var(--color-error-bg)] text-[var(--color-error-fg)] text-sm rounded-md p-3 mb-4">{error}</div>
-		{/if}
+		{#if error}<ErrorBanner message={error} />{/if}
 		<form onsubmit={save} class="space-y-3">
 			<div>
 				<label class="block text-sm font-medium mb-1">{t('actions.provider')}</label>
@@ -242,7 +241,7 @@
 					</label>
 					<label class="flex items-center gap-1 text-sm">
 						<input type="radio" name="schedule_type" value="cron" bind:group={form.schedule_type} class="accent-[var(--color-primary)]" />
-						Cron
+						{t('actions.cronMode')}
 					</label>
 				</div>
 				{#if form.schedule_type === 'interval'}
@@ -263,10 +262,9 @@
 				<label for="act-enabled" class="text-sm">{t('actions.enabled')}</label>
 			</div>
 
-			<button type="submit" disabled={submitting}
-				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">
+			<Button type="submit" disabled={submitting}>
 				{submitting ? t('common.loading') : (editing ? t('common.save') : t('actions.addAction'))}
-			</button>
+			</Button>
 		</form>
 
 		{#if editing}