build: add dev startup scripts and project docs

添加了Windows的start.bat和Linux/macOS的start.sh一键启动脚本，补充了完整的项目README文档，同时修复了前端类型文件的导入路径问题

start.bat

@@ -0,0 +1,62 @@
+@echo off
+title jiang13-bbs launcher
+
+echo ============================================
+echo   jiang13-bbs Dev Launcher
+echo ============================================
+echo.
+
+REM ---- 1. Start PostgreSQL ----
+echo [1/3] Starting database (Docker Compose)...
+docker compose up -d postgres
+if errorlevel 1 (
+    echo [FAIL] Database failed to start. Is Docker running?
+    pause
+    exit /b 1
+)
+echo [OK] Database started
+echo.
+
+REM ---- 2. Backend ----
+echo [2/3] Checking backend config...
+if not exist "backend\app.ini" (
+    copy "backend\app.ini.example" "backend\app.ini" >nul
+    echo   Created backend\app.ini from template
+)
+if not exist "backend\data" mkdir "backend\data"
+
+echo   Starting backend (port 3001)...
+start "jiang13-backend" cmd /k "cd /d %~dp0backend && go run ./cmd/jiang13"
+echo [OK] Backend started
+echo.
+
+REM ---- 3. Frontend ----
+echo [3/3] Checking frontend config...
+if not exist "frontend\.env.local" (
+    copy "frontend\.env.example" "frontend\.env.local" >nul
+    echo   Created frontend\.env.local from template
+)
+
+if not exist "frontend\node_modules" (
+    echo   First run, installing dependencies...
+    cd /d %~dp0frontend
+    call npm install
+    cd /d %~dp0
+)
+
+echo   Starting frontend (port 3000)...
+start "jiang13-frontend" cmd /k "cd /d %~dp0frontend && npm run dev"
+echo [OK] Frontend started
+echo.
+
+echo ============================================
+echo   All services started!
+echo.
+echo   Frontend:  http://localhost:3000
+echo   Backend:   http://localhost:3001
+echo   Database:  localhost:5432
+echo.
+echo   Close each window to stop the service.
+echo   Stop database: docker compose down
+echo ============================================
+pause