chore: add Windows backend startup script

start-backend.bat

@@ -0,0 +1,70 @@
+@echo off
+setlocal EnableExtensions DisableDelayedExpansion
+
+set "PROJECT_ROOT=%~dp0"
+set "BACKEND_ROOT=%PROJECT_ROOT%backend-api"
+
+if not "%~1"=="" if /i not "%~1"=="--migrate" (
+    echo Usage: %~nx0 [--migrate]
+    echo   --migrate  Apply pending database migrations before starting the API.
+    exit /b 2
+)
+
+if not exist "%BACKEND_ROOT%\go.mod" (
+    echo Missing backend project: "%BACKEND_ROOT%"
+    exit /b 1
+)
+
+where go >nul 2>nul
+if errorlevel 1 (
+    echo Go 1.23.0 is required but was not found on PATH.
+    exit /b 1
+)
+
+set "GOTOOLCHAIN=local"
+set "CGO_ENABLED=1"
+for /f "tokens=3" %%G in ('go version') do set "GO_VERSION=%%G"
+if /i not "%GO_VERSION%"=="go1.23.0" (
+    echo Go 1.23.0 is required. Current version: %GO_VERSION%
+    exit /b 1
+)
+
+where gcc >nul 2>nul
+if errorlevel 1 (
+    echo GCC is required because the SQLite driver uses CGO.
+    exit /b 1
+)
+
+pushd "%BACKEND_ROOT%"
+if errorlevel 1 (
+    echo Cannot enter backend directory: "%BACKEND_ROOT%"
+    exit /b 1
+)
+
+if not exist "var" mkdir "var"
+if errorlevel 1 goto :startup_failed
+if not exist "var\assets" mkdir "var\assets"
+if errorlevel 1 goto :startup_failed
+
+if /i "%~1"=="--migrate" (
+    echo Applying database migrations...
+    go run ./cmd/migrate up
+    if errorlevel 1 goto :startup_failed
+)
+
+if defined CMROUBAO_HTTP_ADDR (
+    echo Starting cmroubao backend with configured CMROUBAO_HTTP_ADDR...
+) else (
+    echo Starting cmroubao backend at 127.0.0.1:8080...
+)
+echo Press Ctrl+C to stop.
+go run ./cmd/api
+set "EXIT_CODE=%ERRORLEVEL%"
+popd
+exit /b %EXIT_CODE%
+
+:startup_failed
+set "EXIT_CODE=%ERRORLEVEL%"
+if "%EXIT_CODE%"=="0" set "EXIT_CODE=1"
+popd
+exit /b %EXIT_CODE%