refactor: migrate sync service and handlers to use ConnectionManager

Updated sync-related code to use ConnectionManager instead of direct
database references:

- SyncService now creates repositories on-demand when connection available
- SyncHandler uses ConnectionManager for lazy DB access
- Added ComponentFilter and ListComponents to localdb for offline queries
- All sync operations check connection status before attempting MariaDB access

This completes the transition to offline-first architecture where all
database access goes through ConnectionManager.

Part of Phase 2.5: Full Offline Mode

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

internal/handlers/sync.go

@@ -8,21 +8,21 @@ import (
 	"time"
 
 	"github.com/gin-gonic/gin"
+	"git.mchus.pro/mchus/quoteforge/internal/db"
 	"git.mchus.pro/mchus/quoteforge/internal/localdb"
 	"git.mchus.pro/mchus/quoteforge/internal/services/sync"
-	"gorm.io/gorm"
 )
 
 // SyncHandler handles sync API endpoints
 type SyncHandler struct {
 	localDB     *localdb.LocalDB
 	syncService *sync.Service
-	mariaDB     *gorm.DB
+	connMgr     *db.ConnectionManager
 	tmpl        *template.Template
 }
 
 // NewSyncHandler creates a new sync handler
-func NewSyncHandler(localDB *localdb.LocalDB, syncService *sync.Service, mariaDB *gorm.DB, templatesPath string) (*SyncHandler, error) {
+func NewSyncHandler(localDB *localdb.LocalDB, syncService *sync.Service, connMgr *db.ConnectionManager, templatesPath string) (*SyncHandler, error) {
 	// Load sync_status partial template
 	partialPath := filepath.Join(templatesPath, "partials", "sync_status.html")
 	tmpl, err := template.ParseFiles(partialPath)
@@ -33,7 +33,7 @@ func NewSyncHandler(localDB *localdb.LocalDB, syncService *sync.Service, mariaDB
 	return &SyncHandler{
 		localDB:     localDB,
 		syncService: syncService,
-		mariaDB:     mariaDB,
+		connMgr:     connMgr,
 		tmpl:        tmpl,
 	}, nil
 }
@@ -109,7 +109,17 @@ func (h *SyncHandler) SyncComponents(c *gin.Context) {
 		return
 	}
 
-	result, err := h.localDB.SyncComponents(h.mariaDB)
+	// Get database connection from ConnectionManager
+	mariaDB, err := h.connMgr.GetDB()
+	if err != nil {
+		c.JSON(http.StatusServiceUnavailable, gin.H{
+			"success": false,
+			"error":   "Database connection failed: " + err.Error(),
+		})
+		return
+	}
+
+	result, err := h.localDB.SyncComponents(mariaDB)
 	if err != nil {
 		slog.Error("component sync failed", "error", err)
 		c.JSON(http.StatusInternalServerError, gin.H{
@@ -181,7 +191,16 @@ func (h *SyncHandler) SyncAll(c *gin.Context) {
 	var componentsSynced, pricelistsSynced int
 
 	// Sync components
-	compResult, err := h.localDB.SyncComponents(h.mariaDB)
+	mariaDB, err := h.connMgr.GetDB()
+	if err != nil {
+		c.JSON(http.StatusServiceUnavailable, gin.H{
+			"success": false,
+			"error":   "Database connection failed: " + err.Error(),
+		})
+		return
+	}
+
+	compResult, err := h.localDB.SyncComponents(mariaDB)
 	if err != nil {
 		slog.Error("component sync failed during full sync", "error", err)
 		c.JSON(http.StatusInternalServerError, gin.H{
@@ -215,16 +234,7 @@ func (h *SyncHandler) SyncAll(c *gin.Context) {
 
 // checkOnline checks if MariaDB is accessible
 func (h *SyncHandler) checkOnline() bool {
-	sqlDB, err := h.mariaDB.DB()
-	if err != nil {
-		return false
-	}
-
-	if err := sqlDB.Ping(); err != nil {
-		return false
-	}
-
-	return true
+	return h.connMgr.IsOnline()
 }
 
 // PushPendingChanges pushes all pending changes to the server