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

API_TEST.md

@@ -0,0 +1,164 @@
+# API Testing Guide
+
+## Base URL
+```
+Development: http://localhost:8080/api
+```
+
+## Connection Management
+
+### List all connections
+```bash
+curl http://localhost:8080/api/connections
+```
+
+### Create a new connection
+```bash
+curl -X POST http://localhost:8080/api/connections \
+  -H "Content-Type: application/json" \
+  -d '{
+    "name": "My Database",
+    "type": "mysql",
+    "host": "localhost",
+    "port": 3306,
+    "username": "root",
+    "password": "password123",
+    "database": "mydb"
+  }'
+```
+
+### Update a connection
+```bash
+curl -X PUT http://localhost:8080/api/connections/{id} \
+  -H "Content-Type: application/json" \
+  -d '{
+    "name": "Updated Name",
+    "host": "new-host.com"
+  }'
+```
+
+### Delete a connection
+```bash
+curl -X DELETE http://localhost:8080/api/connections/{id}
+```
+
+### Test connection
+```bash
+curl -X POST http://localhost:8080/api/connections/{id}/test
+```
+
+## Query Operations
+
+### Execute a query
+```bash
+curl -X POST http://localhost:8080/api/query \
+  -H "Content-Type: application/json" \
+  -d '{
+    "connectionId": "{connection-id}",
+    "sql": "SELECT * FROM users LIMIT 10"
+  }'
+```
+
+### Get tables from a connection
+```bash
+curl http://localhost:8080/api/connections/{id}/tables
+```
+
+### Get table data
+```bash
+curl "http://localhost:8080/api/connections/{id}/tables/users/data?limit=20&offset=0"
+```
+
+### Get table structure
+```bash
+curl http://localhost:8080/api/connections/{id}/tables/users/structure
+```
+
+## Saved Queries
+
+### List saved queries
+```bash
+curl http://localhost:8080/api/saved-queries
+```
+
+### Save a query
+```bash
+curl -X POST http://localhost:8080/api/saved-queries \
+  -H "Content-Type: application/json" \
+  -d '{
+    "name": "Daily Users Report",
+    "sql": "SELECT * FROM users WHERE created_at > NOW() - INTERVAL 1 DAY",
+    "connectionId": "{connection-id}"
+  }'
+```
+
+### Execute saved query
+```bash
+curl -X POST http://localhost:8080/api/saved-queries/{id}/execute
+```
+
+## Query History
+
+### Get query history
+```bash
+curl http://localhost:8080/api/history?limit=50
+```
+
+### Clear query history
+```bash
+curl -X DELETE http://localhost:8080/api/history
+```
+
+## Response Format
+
+All responses follow this format:
+
+### Success
+```json
+{
+  "success": true,
+  "data": { ... },
+  "message": ""
+}
+```
+
+### Error
+```json
+{
+  "success": false,
+  "data": null,
+  "error": "Error message here",
+  "code": "CONNECTION_NOT_FOUND"
+}
+```
+
+## Using Wails Bindings (from Frontend)
+
+```javascript
+// Import Wails runtime
+import { Events } from "@wailsio/runtime";
+
+// Get all connections
+const connections = await window.go.app.GetConnections();
+
+// Create connection
+await window.go.app.CreateConnection({
+  name: "Test DB",
+  type: "mysql",
+  host: "localhost",
+  port: 3306,
+  username: "root",
+  password: "secret",
+  database: "test"
+});
+
+// Execute query
+const result = await window.go.app.ExecuteQuery(
+  connectionId,
+  "SELECT * FROM users"
+);
+
+console.log("Rows:", result.rows);
+console.log("Columns:", result.columns);
+console.log("Execution time:", result.executionTimeMs);
+```