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

test-api.sh

@@ -0,0 +1,14 @@
+# Quick start for testing connections and queries
+
+curl -X GET http://localhost:8080/api/connections
+curl -X POST http://localhost:8080/api/connections \
+  -H "Content-Type: application/json" \
+  -d '{
+    "name": "Test MySQL",
+    "type": "mysql",
+    "host": "localhost",
+    "port": 3306,
+    "username": "root",
+    "password": "password",
+    "database": "test"
+  }'