refactor: Flatten directory structure

Move project files from uzdb/ subdirectory to root directory for cleaner project structure.

Changes:
- Move frontend/ to root
- Move internal/ to root
- Move build/ to root
- Move all config files (go.mod, wails.json, etc.) to root
- Remove redundant uzdb/ subdirectory nesting

Project structure is now:
├── frontend/        # React application
├── internal/        # Go backend
├── build/           # Wails build assets
├── doc/             # Design documentation
├── main.go          # Entry point
└── ...

🤖 Generated with Qoder

internal/models/connection.go

@@ -0,0 +1,85 @@
+package models
+
+import (
+	"time"
+)
+
+// ConnectionType represents the type of database connection
+type ConnectionType string
+
+const (
+	// ConnectionTypeMySQL represents MySQL database
+	ConnectionTypeMySQL ConnectionType = "mysql"
+	// ConnectionTypePostgreSQL represents PostgreSQL database
+	ConnectionTypePostgreSQL ConnectionType = "postgres"
+	// ConnectionTypeSQLite represents SQLite database
+	ConnectionTypeSQLite ConnectionType = "sqlite"
+)
+
+// UserConnection represents a user's database connection configuration
+// This model is stored in the local SQLite database
+type UserConnection struct {
+	ID        string    `gorm:"type:varchar(36);primaryKey" json:"id"`
+	Name      string    `gorm:"type:varchar(100);not null" json:"name"`
+	Type      ConnectionType `gorm:"type:varchar(20);not null" json:"type"`
+	Host      string    `gorm:"type:varchar(255)" json:"host,omitempty"`
+	Port      int       `gorm:"type:integer" json:"port,omitempty"`
+	Username  string    `gorm:"type:varchar(100)" json:"username,omitempty"`
+	Password  string    `gorm:"type:text" json:"password"` // Encrypted password
+	Database  string    `gorm:"type:varchar(255)" json:"database"`
+	SSLMode   string    `gorm:"type:varchar(50)" json:"ssl_mode,omitempty"`
+	Timeout   int       `gorm:"type:integer;default:30" json:"timeout"`
+	CreatedAt time.Time `gorm:"autoCreateTime" json:"created_at"`
+	UpdatedAt time.Time `gorm:"autoUpdateTime" json:"updated_at"`
+
+	// For SQLite connections, Database field contains the file path
+}
+
+// TableName returns the table name for UserConnection
+func (UserConnection) TableName() string {
+	return "user_connections"
+}
+
+// CreateConnectionRequest represents a request to create a new connection
+type CreateConnectionRequest struct {
+	Name     string         `json:"name" binding:"required"`
+	Type     ConnectionType `json:"type" binding:"required"`
+	Host     string         `json:"host"`
+	Port     int            `json:"port"`
+	Username string         `json:"username"`
+	Password string         `json:"password"`
+	Database string         `json:"database" binding:"required"`
+	SSLMode  string         `json:"ssl_mode"`
+	Timeout  int            `json:"timeout"`
+}
+
+// UpdateConnectionRequest represents a request to update an existing connection
+type UpdateConnectionRequest struct {
+	Name     string         `json:"name"`
+	Type     ConnectionType `json:"type"`
+	Host     string         `json:"host"`
+	Port     int            `json:"port"`
+	Username string         `json:"username"`
+	Password string         `json:"password"`
+	Database string         `json:"database"`
+	SSLMode  string         `json:"ssl_mode"`
+	Timeout  int            `json:"timeout"`
+}
+
+// Validate validates the connection request
+func (r *CreateConnectionRequest) Validate() error {
+	switch r.Type {
+	case ConnectionTypeMySQL, ConnectionTypePostgreSQL:
+		if r.Host == "" {
+			return ErrValidationFailed
+		}
+		if r.Port <= 0 || r.Port > 65535 {
+			return ErrValidationFailed
+		}
+	case ConnectionTypeSQLite:
+		if r.Database == "" {
+			return ErrValidationFailed
+		}
+	}
+	return nil
+}