feat(notify-bridge): phase 6 - database models and server API

New database schema with ServiceProvider abstraction:
- ServiceProvider (replaces ImmichServer): type + JSON config
- Tracker (replaces AlbumTracker): owns tracking_config_id
- TrackingConfig: provider_type scoped, owned by Tracker
- TemplateConfig: provider_type scoped, owned by Target
- NotificationTarget: owns template_config_id (not tracking_config_id)
- TrackerState, EventLog, User, TelegramBot, TelegramChat

Full FastAPI server:
- /api/providers: CRUD + test connection + list collections
- /api/trackers: CRUD
- /api/tracking-configs: CRUD with provider_type filter
- /api/template-configs: CRUD with provider_type filter, system defaults
- /api/targets: CRUD
- /api/template-vars: variable docs filtered by provider type
- /api/auth: setup, login, refresh, me, password change
- /api/health: health check
- Default template seeding on first startup (EN/RU for Immich)
- pydantic-settings with NOTIFY_BRIDGE_ env prefix

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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

@@ -0,0 +1,33 @@
+"""Template variable documentation endpoint."""
+
+from fastapi import APIRouter
+
+from notify_bridge_core.providers.base import ServiceProviderType
+from notify_bridge_core.providers.immich import ImmichServiceProvider  # noqa: F401 — triggers registration
+from notify_bridge_core.templates.variables import registry
+
+router = APIRouter(prefix="/api/template-vars", tags=["template-vars"])
+
+
+@router.get("")
+async def get_template_variables(provider_type: str | None = None):
+    """Get available template variables, optionally filtered by provider type."""
+    if provider_type:
+        try:
+            pt = ServiceProviderType(provider_type)
+        except ValueError:
+            return {"error": f"Unknown provider type: {provider_type}"}
+        variables = registry.get_variables(pt)
+    else:
+        variables = registry.get_base_variables()
+
+    return [
+        {
+            "name": v.name,
+            "type": v.type,
+            "description": v.description,
+            "example": v.example,
+            "provider_type": v.provider_type.value if v.provider_type else None,
+        }
+        for v in variables
+    ]