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/command-trackers/+page.svelte

@@ -18,6 +18,7 @@
 	import { highlightFromUrl } from '$lib/highlight';
 	import { globalProviderFilter } from '$lib/stores/provider-filter.svelte';
 	import { providerDefaultIcon } from '$lib/grid-items';
+	import Button from '$lib/components/Button.svelte';
 	import type { ServiceProvider, TelegramBot } from '$lib/types';
 
 	let allCmdTrackers = $state<any[]>([]);
@@ -186,10 +187,9 @@
 </script>
 
 <PageHeader title={t('commandTracker.title')} description={t('commandTracker.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('commandTracker.newTracker')}
-	</button>
+	</Button>
 </PageHeader>
 
 {#if !loaded}<Loading />{:else}
@@ -217,10 +217,9 @@
 				<EntitySelect items={configItems} bind:value={form.command_config_id} placeholder={t('commandTracker.selectCommandConfig')} />
 			</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('common.create'))}
-			</button>
+			</Button>
 		</form>
 	</Card>
 {/if}
@@ -257,8 +256,8 @@
 							<CrossLink href="/providers" icon="mdiServer" label={providerName(trk.provider_id)} entityId={trk.provider_id} />
 							<CrossLink href="/command-configs" icon="mdiCog" label={configName(trk.command_config_id)} entityId={trk.command_config_id} />
 							<span class="text-xs px-1.5 py-0.5 rounded font-mono {trk.enabled
-								? 'bg-emerald-500/10 text-emerald-500'
-								: 'bg-red-500/10 text-red-500'}">
+								? 'bg-[var(--color-success-bg)] text-[var(--color-success-fg)]'
+								: 'bg-[var(--color-error-bg)] text-[var(--color-error-fg)]'}">
 								{trk.enabled ? t('commandTracker.enabled') : t('commandTracker.disabled')}
 							</span>
 						</div>
@@ -293,7 +292,7 @@
 										<div class="flex items-center gap-2">
 											<MdiIcon name="mdiRobot" size={14} />
 											<CrossLink href="/bots?tab=telegram" icon="mdiRobot" label={listener.name || listener.listener_type} entityId={listener.listener_id} />
-											<span class="text-xs px-1.5 py-0.5 rounded bg-blue-500/10 text-blue-500 font-mono">{listener.listener_type}</span>
+											<span class="text-xs px-1.5 py-0.5 rounded bg-[var(--color-primary)]/10 text-[var(--color-primary)] font-mono">{listener.listener_type}</span>
 										</div>
 										<IconButton icon="mdiClose" title={t('commandTracker.removeListener')} size={14}
 											onclick={() => removeListener(trk.id, listener.id)} variant="danger" />
@@ -307,10 +306,9 @@
 							<div class="flex-1">
 								<EntitySelect items={botItems} bind:value={newListenerBotId[trk.id]} placeholder={t('commandTracker.selectBot')} />
 							</div>
-							<button onclick={() => addListener(trk.id)} disabled={!newListenerBotId[trk.id] || addingListener[trk.id]}
-								class="text-xs px-3 py-1 bg-[var(--color-primary)] text-[var(--color-primary-foreground)] rounded-md hover:opacity-90 disabled:opacity-50">
+							<Button size="sm" onclick={() => addListener(trk.id)} disabled={!newListenerBotId[trk.id] || addingListener[trk.id]}>
 								{addingListener[trk.id] ? t('common.loading') : t('commandTracker.addListener')}
-							</button>
+							</Button>
 						</div>
 					</div>
 				{/if}