Add Phase 2: Local SQLite database with sync functionality

Implements complete offline-first architecture with SQLite caching and MariaDB synchronization.

Key features:
- Local SQLite database for offline operation (data/quoteforge.db)
- Connection settings with encrypted credentials
- Component and pricelist caching with auto-sync
- Sync API endpoints (/api/sync/status, /components, /pricelists, /all)
- Real-time sync status indicator in UI with auto-refresh
- Offline mode detection middleware
- Migration tool for database initialization
- Setup wizard for initial configuration

New components:
- internal/localdb: SQLite repository layer (components, pricelists, sync)
- internal/services/sync: Synchronization service
- internal/handlers/sync: Sync API handlers
- internal/handlers/setup: Setup wizard handlers
- internal/middleware/offline: Offline detection
- cmd/migrate: Database migration tool

UI improvements:
- Setup page for database configuration
- Sync status indicator with online/offline detection
- Warning icons for pending synchronization
- Auto-refresh every 30 seconds

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

internal/handlers/setup.go

@@ -0,0 +1,196 @@
+package handlers
+
+import (
+	"fmt"
+	"html/template"
+	"net/http"
+	"path/filepath"
+	"strconv"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"git.mchus.pro/mchus/quoteforge/internal/localdb"
+	"gorm.io/driver/mysql"
+	"gorm.io/gorm"
+	"gorm.io/gorm/logger"
+)
+
+type SetupHandler struct {
+	localDB   *localdb.LocalDB
+	templates map[string]*template.Template
+}
+
+func NewSetupHandler(localDB *localdb.LocalDB, templatesPath string) (*SetupHandler, error) {
+	funcMap := template.FuncMap{
+		"sub": func(a, b int) int { return a - b },
+		"add": func(a, b int) int { return a + b },
+	}
+
+	templates := make(map[string]*template.Template)
+
+	// Load setup template (standalone, no base needed)
+	setupPath := filepath.Join(templatesPath, "setup.html")
+	tmpl, err := template.New("").Funcs(funcMap).ParseFiles(setupPath)
+	if err != nil {
+		return nil, fmt.Errorf("parsing setup template: %w", err)
+	}
+	templates["setup.html"] = tmpl
+
+	return &SetupHandler{
+		localDB:   localDB,
+		templates: templates,
+	}, nil
+}
+
+// ShowSetup renders the database setup form
+func (h *SetupHandler) ShowSetup(c *gin.Context) {
+	c.Header("Content-Type", "text/html; charset=utf-8")
+
+	// Get existing settings if any
+	settings, _ := h.localDB.GetSettings()
+
+	data := gin.H{
+		"Settings": settings,
+	}
+
+	tmpl := h.templates["setup.html"]
+	if err := tmpl.ExecuteTemplate(c.Writer, "setup.html", data); err != nil {
+		c.String(http.StatusInternalServerError, "Template error: %v", err)
+	}
+}
+
+// TestConnection tests the database connection without saving
+func (h *SetupHandler) TestConnection(c *gin.Context) {
+	host := c.PostForm("host")
+	portStr := c.PostForm("port")
+	database := c.PostForm("database")
+	user := c.PostForm("user")
+	password := c.PostForm("password")
+
+	port := 3306
+	if p, err := strconv.Atoi(portStr); err == nil {
+		port = p
+	}
+
+	dsn := fmt.Sprintf("%s:%s@tcp(%s:%d)/%s?charset=utf8mb4&parseTime=True&loc=Local&timeout=5s",
+		user, password, host, port, database)
+
+	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{
+		Logger: logger.Default.LogMode(logger.Silent),
+	})
+	if err != nil {
+		c.JSON(http.StatusOK, gin.H{
+			"success": false,
+			"error":   fmt.Sprintf("Connection failed: %v", err),
+		})
+		return
+	}
+
+	sqlDB, err := db.DB()
+	if err != nil {
+		c.JSON(http.StatusOK, gin.H{
+			"success": false,
+			"error":   fmt.Sprintf("Failed to get database handle: %v", err),
+		})
+		return
+	}
+	defer sqlDB.Close()
+
+	if err := sqlDB.Ping(); err != nil {
+		c.JSON(http.StatusOK, gin.H{
+			"success": false,
+			"error":   fmt.Sprintf("Ping failed: %v", err),
+		})
+		return
+	}
+
+	// Check for required tables
+	var lotCount int64
+	if err := db.Table("lot").Count(&lotCount).Error; err != nil {
+		c.JSON(http.StatusOK, gin.H{
+			"success": false,
+			"error":   fmt.Sprintf("Table 'lot' not found or inaccessible: %v", err),
+		})
+		return
+	}
+
+	// Check write permission
+	canWrite := testWritePermission(db)
+
+	c.JSON(http.StatusOK, gin.H{
+		"success":   true,
+		"lot_count": lotCount,
+		"can_write": canWrite,
+		"message":   fmt.Sprintf("Connected successfully! Found %d components.", lotCount),
+	})
+}
+
+// SaveConnection saves the connection settings and signals restart
+func (h *SetupHandler) SaveConnection(c *gin.Context) {
+	host := c.PostForm("host")
+	portStr := c.PostForm("port")
+	database := c.PostForm("database")
+	user := c.PostForm("user")
+	password := c.PostForm("password")
+
+	port := 3306
+	if p, err := strconv.Atoi(portStr); err == nil {
+		port = p
+	}
+
+	// Test connection first
+	dsn := fmt.Sprintf("%s:%s@tcp(%s:%d)/%s?charset=utf8mb4&parseTime=True&loc=Local&timeout=5s",
+		user, password, host, port, database)
+
+	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{
+		Logger: logger.Default.LogMode(logger.Silent),
+	})
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{
+			"success": false,
+			"error":   fmt.Sprintf("Connection failed: %v", err),
+		})
+		return
+	}
+
+	sqlDB, _ := db.DB()
+	sqlDB.Close()
+
+	// Save settings
+	if err := h.localDB.SaveSettings(host, port, database, user, password); err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{
+			"success": false,
+			"error":   fmt.Sprintf("Failed to save settings: %v", err),
+		})
+		return
+	}
+
+	c.JSON(http.StatusOK, gin.H{
+		"success": true,
+		"message": "Settings saved. Please restart the application.",
+	})
+}
+
+// GetStatus returns the current setup status
+func (h *SetupHandler) GetStatus(c *gin.Context) {
+	hasSettings := h.localDB.HasSettings()
+	c.JSON(http.StatusOK, gin.H{
+		"configured": hasSettings,
+	})
+}
+
+func testWritePermission(db *gorm.DB) bool {
+	// Simple check: try to create a temporary table and drop it
+	testTable := fmt.Sprintf("qt_write_test_%d", time.Now().UnixNano())
+
+	// Try to create a test table
+	err := db.Exec(fmt.Sprintf("CREATE TABLE %s (id INT)", testTable)).Error
+	if err != nil {
+		return false
+	}
+
+	// Drop it immediately
+	db.Exec(fmt.Sprintf("DROP TABLE %s", testTable))
+
+	return true
+}