fix: move email-in-address endpoint from /auth to /api/v1 prefix

The GET /me/email-in-address endpoint was unreachable because the Gateway
HTTPRoute routes all /auth/* traffic to Better-Auth (port 3001), not the
API service. This change:
- Moves the endpoint from the /auth router to a new /api/v1/me/ router
- Adds EmailInAddressResponse schema and get_email_in_address service method
- Updates Settings.tsx to call /api/v1/me/email-in-address

Fixes CAR-445.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/cartsnitch_api/routes/user.py

@@ -0,0 +1,26 @@
+"""User routes: per-user account endpoints (email-in address, etc.)."""
+
+from fastapi import APIRouter, Depends, HTTPException, status
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from cartsnitch_api.auth.dependencies import get_current_user
+from cartsnitch_api.database import get_db
+from cartsnitch_api.schemas import EmailInAddressResponse
+from cartsnitch_api.services.auth import AuthService
+
+router = APIRouter(tags=["user"])
+
+
+@router.get("/me/email-in-address", response_model=EmailInAddressResponse)
+async def get_email_in_address(
+    user_id: str = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    svc = AuthService(db)
+    try:
+        email_address = await svc.get_email_in_address(user_id)
+        return EmailInAddressResponse(email_address=email_address)
+    except LookupError:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND, detail="User not found"
+        ) from None