feat: Migrate to MySQL and add unified environment configuration

## Database Migration (SQLite → MySQL)
- Add Alembic migration framework
- Add 'tr_' prefix to all tables to avoid conflicts in shared database
- Remove SQLite support, use MySQL exclusively
- Add pymysql driver dependency
- Change ad_token column to Text type for long JWT tokens

## Unified Environment Configuration
- Centralize all hardcoded settings to environment variables
- Backend: Extend Settings class in app/core/config.py
- Frontend: Use Vite environment variables (import.meta.env)
- Docker: Move credentials to environment variables
- Update .env.example files with comprehensive documentation

## Test Organization
- Move root-level test files to tests/ directory:
  - test_chat_room.py → tests/test_chat_room.py
  - test_websocket.py → tests/test_websocket.py
  - test_realtime_implementation.py → tests/test_realtime_implementation.py
- Fix path references in test_realtime_implementation.py

Breaking Changes:
- CORS now requires explicit origins (no more wildcard)
- All database tables renamed with 'tr_' prefix
- SQLite no longer supported

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/vite.config.ts

@@ -1,28 +1,36 @@
 /// <reference types="vitest/config" />
-import { defineConfig } from 'vite'
+import { defineConfig, loadEnv } from 'vite'
 import react from '@vitejs/plugin-react'
 import tailwindcss from '@tailwindcss/vite'
 
 // https://vite.dev/config/
-export default defineConfig({
-  plugins: [
-    tailwindcss(),
-    react(),
-  ],
-  server: {
-    port: 3000,
-    proxy: {
-      '/api': {
-        target: 'http://localhost:8000',
-        changeOrigin: true,
-        ws: true, // Enable WebSocket proxying
+export default defineConfig(({ mode }) => {
+  const env = loadEnv(mode, process.cwd(), '')
+
+  // Configuration from environment variables with defaults
+  const PORT = parseInt(env.VITE_PORT || '3000', 10)
+  const BACKEND_URL = env.VITE_BACKEND_URL || 'http://localhost:8000'
+
+  return {
+    plugins: [
+      tailwindcss(),
+      react(),
+    ],
+    server: {
+      port: PORT,
+      proxy: {
+        '/api': {
+          target: BACKEND_URL,
+          changeOrigin: true,
+          ws: true, // Enable WebSocket proxying
+        },
       },
     },
-  },
-  test: {
-    globals: true,
-    environment: 'jsdom',
-    setupFiles: ['./src/test/setup.ts'],
-    include: ['src/**/*.{test,spec}.{js,mjs,cjs,ts,mts,cts,jsx,tsx}'],
-  },
+    test: {
+      globals: true,
+      environment: 'jsdom',
+      setupFiles: ['./src/test/setup.ts'],
+      include: ['src/**/*.{test,spec}.{js,mjs,cjs,ts,mts,cts,jsx,tsx}'],
+    },
+  }
 })