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

packages/server/src/notify_bridge_server/api/delete_protection.py

@@ -15,8 +15,6 @@ from ..database.models import (
     NotificationTarget,
     NotificationTracker,
     NotificationTrackerTarget,
-    TargetReceiver,
-    TelegramChat,
 )
 
 
@@ -164,16 +162,3 @@ async def check_notification_target(session: AsyncSession, target_id: int) -> li
     return consumers
 
 
-async def check_notification_tracker(session: AsyncSession, tracker_id: int) -> list[str]:
-    """Check if a NotificationTracker has any linked targets."""
-    consumers = []
-    result = await session.exec(
-        select(NotificationTrackerTarget).where(
-            NotificationTrackerTarget.tracker_id == tracker_id
-        )
-    )
-    for tt in result.all():
-        target = await session.get(NotificationTarget, tt.target_id)
-        name = target.name if target else f"#{tt.target_id}"
-        consumers.append(f"Linked Target: {name}")
-    return consumers