Add backend foundation and config-driven workbench

backend/.env.example

@@ -0,0 +1,20 @@
+APP_ENV=development
+HTTP_ADDR=:8080
+DATABASE_URL=postgres://postgres:asdf*123@192.168.100.77:5432/cmr20260401?sslmode=disable
+
+JWT_ISSUER=cmr-backend
+JWT_ACCESS_SECRET=change-me-in-production
+JWT_ACCESS_TTL=2h
+AUTH_REFRESH_TTL=720h
+
+AUTH_SMS_CODE_TTL=10m
+AUTH_SMS_COOLDOWN=60s
+AUTH_SMS_PROVIDER=console
+AUTH_DEV_SMS_CODE=
+
+WECHAT_MINI_APP_ID=
+WECHAT_MINI_APP_SECRET=
+WECHAT_MINI_DEV_PREFIX=dev-
+
+LOCAL_EVENT_DIR=..\event
+ASSET_BASE_URL=https://oss-mbh5.colormaprun.com/gotomars