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/bots/TelegramBotTab.svelte

@@ -303,10 +303,9 @@
 					class="w-full px-3 py-2 border border-[var(--color-border)] rounded-md text-sm bg-[var(--color-background)] font-mono" />
 			</div>
 			{/if}
-			<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('telegramBot.addBot'))}
-			</button>
+			</Button>
 		</form>
 	</Card>
 {/if}
@@ -329,8 +328,8 @@
 							{/if}
 							<!-- Mode badge -->
 							<span class="text-xs px-1.5 py-0.5 rounded font-mono {bot.update_mode === 'webhook'
-								? 'bg-blue-500/10 text-blue-500'
-								: 'bg-emerald-500/10 text-emerald-500'}">
+								? 'bg-[var(--color-primary)]/10 text-[var(--color-primary)]'
+								: 'bg-[var(--color-success-bg)] text-[var(--color-success-fg)]'}">
 								{bot.update_mode === 'webhook' ? t('telegramBot.webhook') : t('telegramBot.polling')}
 							</span>
 						</div>
@@ -378,7 +377,7 @@
 									onclick={(e: MouseEvent) => copyChatId(e, chat.chat_id)}
 									title={t('telegramBot.clickToCopy')}
 									role="button" tabindex="0">
-									<span class="font-medium truncate">{chat.title || chat.username || 'Unknown'}</span>
+									<span class="font-medium truncate">{chat.title || chat.username || t('common.unknown')}</span>
 									<span style="text-align:center" class="text-xs px-1.5 py-0.5 rounded bg-[var(--color-muted)] text-[var(--color-muted-foreground)]">{chatTypeLabel(chat.type)}</span>
 									<span style="text-align:center" class="text-xs text-[var(--color-muted-foreground)]">{(chat.language_code || '—').toUpperCase()}</span>
 									<div style="justify-self:center" onclick={(e: MouseEvent) => e.stopPropagation()}>
@@ -399,7 +398,7 @@
 									</div>
 									<span style="text-align:center" class="text-xs text-[var(--color-muted-foreground)] font-mono">{chat.chat_id}</span>
 									<div style="justify-self:end" class="flex items-center gap-1">
-										<IconButton icon="mdiSend" title="Test message" size={14}
+										<IconButton icon="mdiSend" title={t('common.test')} size={14}
 											onclick={(e: MouseEvent) => testChat(e, bot.id, chat.chat_id)}
 											disabled={chatTesting[`${bot.id}_${chat.chat_id}`]} />
 										<IconButton icon="mdiDelete" title={t('common.delete')} size={14}
@@ -465,7 +464,7 @@
 								</div>
 
 								{#if bot.update_mode === 'polling'}
-									<span class="text-xs text-emerald-500 flex items-center gap-1">
+									<span class="text-xs text-[var(--color-success-fg)] flex items-center gap-1">
 										<MdiIcon name="mdiCheckCircle" size={14} />
 										{t('telegramBot.pollingActive')}
 									</span>
@@ -489,7 +488,7 @@
 											{/if}
 										</span>
 										{#if ws.last_error_message}
-											<span class="text-xs text-red-500">{t('telegramBot.webhookError')}: {ws.last_error_message}</span>
+											<span class="text-xs text-[var(--color-error-fg)]">{t('telegramBot.webhookError')}: {ws.last_error_message}</span>
 										{/if}
 									{:else}
 										<button onclick={() => loadWebhookStatus(bot.id)}
@@ -500,7 +499,7 @@
 								{/if}
 
 								{#if !settings.external_url && bot.update_mode === 'webhook'}
-									<span class="text-xs text-amber-500 flex items-center gap-1">
+									<span class="text-xs text-[var(--color-warning-fg)] flex items-center gap-1">
 										<MdiIcon name="mdiAlert" size={14} />
 										{t('telegramBot.noExternalDomain')}
 									</span>