fix: improve friendships schemas type safety and consistency

backend/src/v1/friendships/schemas.py

@@ -1,38 +1,42 @@
 from __future__ import annotations
 from datetime import datetime
-from typing import Optional
+from typing import ClassVar, Literal
 from uuid import UUID
 
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, ConfigDict, Field
 
 
 class UserBasicInfo(BaseModel):
     id: str
     username: str
-    avatar_url: Optional[str] = None
+    avatar_url: str | None = None
 
 
 class FriendRequestCreate(BaseModel):
+    model_config: ClassVar[ConfigDict] = ConfigDict(extra="forbid")
+
     target_user_id: UUID
-    content: Optional[str] = Field(None, max_length=200)
+    content: str | None = Field(None, max_length=200)
 
 
 class FriendRequestResponse(BaseModel):
     id: UUID
     sender: UserBasicInfo
     recipient: UserBasicInfo
-    content: Optional[str]
-    status: str
+    content: str | None
+    status: Literal["pending", "accepted", "rejected"]
     created_at: datetime
 
 
 class FriendResponse(BaseModel):
     id: UUID
     friend: UserBasicInfo
-    status: str
+    status: Literal["active"]
     created_at: datetime
-    accepted_at: Optional[datetime]
+    accepted_at: datetime | None
 
 
 class FriendRequestAction(BaseModel):
+    model_config: ClassVar[ConfigDict] = ConfigDict(extra="forbid")
+
     pass