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/query.go

@@ -0,0 +1,58 @@
+package models
+
+import (
+	"time"
+)
+
+// QueryHistory represents a record of executed queries
+type QueryHistory struct {
+	ID            uint      `gorm:"primaryKey" json:"id"`
+	ConnectionID  string    `gorm:"type:varchar(36);not null;index" json:"connection_id"`
+	SQL           string    `gorm:"type:text;not null" json:"sql"`
+	Duration      int64     `gorm:"type:bigint" json:"duration_ms"` // Duration in milliseconds
+	ExecutedAt    time.Time `gorm:"autoCreateTime;index" json:"executed_at"`
+	RowsAffected  int64     `gorm:"type:bigint" json:"rows_affected"`
+	Error         string    `gorm:"type:text" json:"error,omitempty"`
+	Success       bool      `gorm:"type:boolean;default:false" json:"success"`
+	ResultPreview string    `gorm:"type:text" json:"result_preview,omitempty"` // JSON preview of first few rows
+}
+
+// TableName returns the table name for QueryHistory
+func (QueryHistory) TableName() string {
+	return "query_history"
+}
+
+// SavedQuery represents a saved SQL query
+type SavedQuery struct {
+	ID          uint      `gorm:"primaryKey" json:"id"`
+	Name        string    `gorm:"type:varchar(255);not null" json:"name"`
+	Description string    `gorm:"type:text" json:"description"`
+	SQL         string    `gorm:"type:text;not null" json:"sql"`
+	ConnectionID string   `gorm:"type:varchar(36);index" json:"connection_id"`
+	Tags        string    `gorm:"type:text" json:"tags"` // Comma-separated tags
+	CreatedAt   time.Time `gorm:"autoCreateTime" json:"created_at"`
+	UpdatedAt   time.Time `gorm:"autoUpdateTime" json:"updated_at"`
+}
+
+// TableName returns the table name for SavedQuery
+func (SavedQuery) TableName() string {
+	return "saved_queries"
+}
+
+// CreateSavedQueryRequest represents a request to save a query
+type CreateSavedQueryRequest struct {
+	Name        string `json:"name" binding:"required"`
+	Description string `json:"description"`
+	SQL         string `json:"sql" binding:"required"`
+	ConnectionID string `json:"connection_id"`
+	Tags        string `json:"tags"`
+}
+
+// UpdateSavedQueryRequest represents a request to update a saved query
+type UpdateSavedQueryRequest struct {
+	Name        string `json:"name"`
+	Description string `json:"description"`
+	SQL         string `json:"sql"`
+	ConnectionID string `json:"connection_id"`
+	Tags        string `json:"tags"`
+}