Add offline RefreshPrices, fix sync bugs, implement auto-restart

- Implement RefreshPrices for local-first mode
  - Update prices from local_components.current_price cache
  - Graceful degradation when component not found
  - Add PriceUpdatedAt timestamp to LocalConfiguration model
  - Support both authenticated and no-auth price refresh

- Fix sync duplicate entry bug
  - pushConfigurationUpdate now ensures server_id exists before update
  - Fetch from LocalConfiguration.ServerID or search on server if missing
  - Update local config with server_id after finding

- Add application auto-restart after settings save
  - Implement restartProcess() using syscall.Exec
  - Setup handler signals restart via channel
  - Setup page polls /health endpoint and redirects when ready
  - Add "Back" button on setup page when settings exist

- Fix setup handler password handling
  - Use PasswordEncrypted field consistently
  - Support empty password by using saved value

- Improve sync status handling
  - Add fallback for is_offline check in SyncStatusPartial
  - Enhance background sync logging with prefixes

- Update CLAUDE.md documentation
  - Mark Phase 2.5 tasks as complete
  - Add UI Improvements section with future tasks
  - Update SQLite tables documentation

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

internal/services/sync/service.go

@@ -337,6 +337,31 @@ func (s *Service) pushConfigurationUpdate(change *localdb.PendingChange) error {
 		return fmt.Errorf("unmarshaling configuration: %w", err)
 	}
 
+	// Ensure we have a server ID before updating
+	// If the payload doesn't have ID, get it from local configuration
+	if cfg.ID == 0 {
+		localCfg, err := s.localDB.GetConfigurationByUUID(cfg.UUID)
+		if err != nil {
+			return fmt.Errorf("getting local configuration: %w", err)
+		}
+
+		if localCfg.ServerID == nil {
+			// Configuration hasn't been synced yet, try to find it on server by UUID
+			serverCfg, err := s.configRepo.GetByUUID(cfg.UUID)
+			if err != nil {
+				return fmt.Errorf("configuration not yet synced to server: %w", err)
+			}
+			cfg.ID = serverCfg.ID
+
+			// Update local with server ID
+			serverID := serverCfg.ID
+			localCfg.ServerID = &serverID
+			s.localDB.SaveConfiguration(localCfg)
+		} else {
+			cfg.ID = *localCfg.ServerID
+		}
+	}
+
 	// Update on server
 	if err := s.configRepo.Update(&cfg); err != nil {
 		return fmt.Errorf("updating configuration on server: %w", err)