Fix LDAP login: ensure password encoding and include user in response

- Fix password encoding: Convert password to UTF-8 bytes for LDAP protocol compatibility
- Add 'user' field to TokenResponse schema for frontend compatibility
- Update login endpoint to populate user object in response
- Resolves 'Invalid Protocol Password' error on LDAP login attempts

The issue was that frontend expected response.user but backend only returned
individual fields (user_id, username, role), causing localStorage assignment to fail.

backend/schemas/users.py

@@ -42,3 +42,4 @@ class TokenResponse(BaseModel):
     user_id: int
     username: str
     role: str
+    user: Optional['User'] = None  # For frontend compatibility