feat(dashboard): implement Phase 7 router registration and config setup

Add DashboardService and DashboardHandler to application configuration:

Router Config Updates (internal/router/router.go):
- Add services import for DashboardService type
- Add DashboardService field to Config struct
- DashboardService: Used by SSR routes in frontend.go for data fetching
- DashboardHandler: Used by API routes in dashboard.go for JSON endpoints

Server Initialization (cmd/server/main.go):
- Create dashboardService instance using services.NewDashboardService(queries)
- Keep dashboardHandler creation (already exists from Phase 4)
- Add DashboardService to routerConfig
- Both services now available for dependency injection

Test Helpers (cmd/server/tests/test_helpers.go):
- Create dashboardService instance for testing
- Create dashboardHandler instance for testing
- Add both DashboardService and DashboardHandler to routerConfig
- Ensures test environment matches production setup

Architecture Rationale:
- DashboardService: Service layer with business logic (reusable by SSR, mobile)
- DashboardHandler: HTTP handler layer (JSON API endpoints)
- Separation allows SSR templates to call service directly
- API routes use handler for proper HTTP response handling
- Mobile apps can use API endpoints via DashboardHandler

All three files updated consistently for complete integration.

cmd/server/main.go

@@ -119,6 +119,7 @@ func main() {
 
 	// NEW: Create refactored handlers
 	collectionHandler := handlers.NewCollectionHandler(queries, connManager)
+	dashboardService := services.NewDashboardService(queries)
 	dashboardHandler := handlers.NewDashboardHandler(queries)
 	mediaHandler := handlers.NewMediaHandler(queries, libraryService, worker)
 	matchingHandler := handlers.NewMatchingHandler(queries, connManager)
@@ -170,6 +171,7 @@ func main() {
 		QueueHandler:          queueHandler,
 		CollectionHandler:     collectionHandler,
 		DashboardHandler:      dashboardHandler,
+		DashboardService:      dashboardService,
 		OPDSHandler:           opdsHandler,
 		SystemSettingsHandler: systemSettingsHandler,
 		ConnManager:           connManager,

cmd/server/tests/test_helpers.go

@@ -411,6 +411,8 @@ func setupTestServer(t *testing.T) *TestServerSetup {
 	libraryService := services.NewLibraryService(queries)
 	worker := services.NewWorker(3)
 	collectionHandler := handlers.NewCollectionHandler(queries, connManager)
+	dashboardService := services.NewDashboardService(queries)
+	dashboardHandler := handlers.NewDashboardHandler(queries)
 	mediaHandler := handlers.NewMediaHandler(queries, libraryService, worker)
 	matchingHandler := handlers.NewMatchingHandler(queries, connManager)
 
@@ -451,6 +453,8 @@ func setupTestServer(t *testing.T) *TestServerSetup {
 		QueueHandler:          queueHandler,
 		SystemSettingsHandler: systemSettingsHandler,
 		CollectionHandler:     collectionHandler,
+		DashboardHandler:      dashboardHandler,
+		DashboardService:      dashboardService,
 		OPDSHandler:           opdsHandler,
 		ConnManager:           connManager,
 		QueueProcessor:        queueProcessor,