refactor: unify test dispatch with real NotificationDispatcher

- Route scheduled/memory test sends through the same NotificationDispatcher
  the watcher uses — identical template rendering, media handling, caching
- Add preview_url field to MediaAsset (transcoded mid-size), separate from
  thumbnail_url (small) and full_url (original). Dispatcher prefers preview_url
- Fix sendMediaGroup cache: extract file_ids from Telegram response and store
  via async_set_many so repeat sends use cached file_ids
- Parallelize asset downloads in _send_media_group with asyncio.gather
- Filter unprocessed assets (archived/trashed/offline/no-thumbhash) at album
  parse time in ImmichAlbumData.from_api_response
- Extract shared asset_to_media + collect_scheduled_assets into asset_utils.py
  (single source for test dispatch and future real scheduler)
- Respect tracking config filters: limit, asset_type, favorite_only, min_rating
- Random asset sampling for scheduled sends
- Memory mode: "On This Day" date filter (same month+day, previous year)
- Skip dispatch when no matching assets found
- Remove ~250 lines of duplicated send logic from notifier.py
- Fix restart-backend.sh: proper env var export, Python path resolution, error log

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

@@ -21,7 +21,8 @@ from ..database.models import (
     TrackingConfig,
     User,
 )
-from ..services.notifier import send_real_data_notification, send_test_notification
+from ..services.notifier import send_test_notification
+from ..services.test_dispatch import dispatch_test_notification
 
 _LOGGER = logging.getLogger(__name__)
 
@@ -242,62 +243,14 @@ async def test_notification_tracker_target(
         r = await send_test_notification(target, locale=effective_locale)
         return {"target": target.name, **r}
 
-    # For periodic/scheduled/memory — fetch real data from provider
-    template_config = None
-    template_str = ""
-    if tt.template_config_id:
-        template_config = await session.get(TemplateConfig, tt.template_config_id)
-        if template_config:
-            slot_map = {
-                "periodic": "periodic_summary_message",
-                "scheduled": "scheduled_assets_message",
-                "memory": "memory_mode_message",
-            }
-            slot_name = slot_map[test_type]
-            slot_result = await session.exec(
-                select(TemplateSlot).where(
-                    TemplateSlot.config_id == template_config.id,
-                    TemplateSlot.slot_name == slot_name,
-                    TemplateSlot.locale == effective_locale,
-                )
-            )
-            slot = slot_result.first()
-            if not slot:
-                # Fallback: any locale
-                slot_result2 = await session.exec(
-                    select(TemplateSlot).where(
-                        TemplateSlot.config_id == template_config.id,
-                        TemplateSlot.slot_name == slot_name,
-                    )
-                )
-                slot = slot_result2.first()
-            template_str = slot.template if slot else ""
-
-    # Load provider and tracker data eagerly before aiohttp context
-    provider = await session.get(ServiceProvider, tracker.provider_id)
-    if not provider:
-        raise HTTPException(status_code=404, detail="Provider not found")
-    provider_config = dict(provider.config)
-    collection_ids = list(tracker.collection_ids or [])
-
-    # Load tracking config to get memory_source
-    memory_source = "albums"
-    if tt.tracking_config_id:
-        tracking_config = await session.get(TrackingConfig, tt.tracking_config_id)
-        if tracking_config:
-            memory_source = tracking_config.memory_source or "albums"
-
-    # Fetch real data from provider
-    r = await send_real_data_notification(
+    # For periodic/scheduled/memory — dispatch through the real NotificationDispatcher
+    r = await dispatch_test_notification(
+        session=session,
+        tracker=tracker,
+        tt=tt,
         target=target,
-        template_str=template_str,
         test_type=test_type,
-        provider_type=provider.type,
-        provider_config=provider_config,
-        collection_ids=collection_ids,
-        date_format=template_config.date_format if template_config else "%d.%m.%Y, %H:%M UTC",
-        date_only_format=template_config.date_only_format if template_config and template_config.date_only_format else "%d.%m.%Y",
-        memory_source=memory_source,
+        locale=effective_locale,
     )
     return {"target": target.name, **r}