feat: add django user center auth integration

backend/app/api/auth.py

@@ -0,0 +1,22 @@
+from fastapi import APIRouter, Depends
+
+from app.core.response import ApiResponse, ok
+from app.core.user_context import UserContext, get_user_context
+from app.schemas.auth import AuthMeResponse
+
+router = APIRouter()
+
+
+@router.get("/me", response_model=ApiResponse[AuthMeResponse])
+async def auth_me(ctx: UserContext = Depends(get_user_context)):
+    """当前用户：返回经 Django 用户中心或 Demo Header 标准化后的用户信息。"""
+    return ok(
+        AuthMeResponse(
+            user_id=ctx.user_id,
+            source=ctx.auth_source,
+            username=ctx.username,
+            display_name=ctx.display_name,
+            tenant_id=ctx.tenant_id,
+            role=ctx.role,
+        )
+    )