feat(friendships): create module structure and schemas

backend/src/v1/friendships/dependencies.py

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+from __future__ import annotations

backend/src/v1/friendships/repository.py

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+from __future__ import annotations

backend/src/v1/friendships/router.py

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+from __future__ import annotations

backend/src/v1/friendships/schemas.py

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+from __future__ import annotations
+from datetime import datetime
+from typing import Optional
+from uuid import UUID
+
+from pydantic import BaseModel, Field
+
+
+class UserBasicInfo(BaseModel):
+    id: str
+    username: str
+    avatar_url: Optional[str] = None
+
+
+class FriendRequestCreate(BaseModel):
+    target_user_id: UUID
+    content: Optional[str] = Field(None, max_length=200)
+
+
+class FriendRequestResponse(BaseModel):
+    id: UUID
+    sender: UserBasicInfo
+    recipient: UserBasicInfo
+    content: Optional[str]
+    status: str
+    created_at: datetime
+
+
+class FriendResponse(BaseModel):
+    id: UUID
+    friend: UserBasicInfo
+    status: str
+    created_at: datetime
+    accepted_at: Optional[datetime]
+
+
+class FriendRequestAction(BaseModel):
+    pass

backend/src/v1/friendships/service.py

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+from __future__ import annotations

backend/tests/unit/v1/friendships/test_schemas.py

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+from __future__ import annotations
+
+import pytest
+from datetime import datetime
+from uuid import uuid4
+
+from v1.friendships.schemas import (
+    UserBasicInfo,
+    FriendRequestCreate,
+    FriendRequestResponse,
+    FriendResponse,
+    FriendRequestAction,
+)
+
+
+def test_user_basic_info_maps_fields() -> None:
+    user = UserBasicInfo(id="user-1", username="alice", avatar_url=None)
+
+    assert user.id == "user-1"
+    assert user.username == "alice"
+    assert user.avatar_url is None
+
+
+def test_user_basic_info_with_avatar() -> None:
+    user = UserBasicInfo(
+        id="user-2", username="bob", avatar_url="https://example.com/avatar.png"
+    )
+
+    assert user.avatar_url == "https://example.com/avatar.png"
+
+
+def test_friend_request_create_valid() -> None:
+    target_id = uuid4()
+    request = FriendRequestCreate(
+        target_user_id=target_id, content="Hi, let's be friends!"
+    )
+
+    assert request.target_user_id == target_id
+    assert request.content == "Hi, let's be friends!"
+
+
+def test_friend_request_create_without_content() -> None:
+    target_id = uuid4()
+    request = FriendRequestCreate(target_user_id=target_id, content=None)
+
+    assert request.target_user_id == target_id
+    assert request.content is None
+
+
+def test_friend_request_create_content_max_length() -> None:
+    target_id = uuid4()
+    with pytest.raises(Exception):
+        FriendRequestCreate(target_user_id=target_id, content="x" * 201)
+
+
+def test_friend_request_response_maps_fields() -> None:
+    sender = UserBasicInfo(id="user-1", username="alice", avatar_url=None)
+    recipient = UserBasicInfo(id="user-2", username="bob", avatar_url=None)
+    request_id = uuid4()
+    created = datetime(2026, 1, 15, 10, 30, 0)
+
+    response = FriendRequestResponse(
+        id=request_id,
+        sender=sender,
+        recipient=recipient,
+        content="Hello!",
+        status="pending",
+        created_at=created,
+    )
+
+    assert response.id == request_id
+    assert response.sender.username == "alice"
+    assert response.recipient.username == "bob"
+    assert response.status == "pending"
+    assert response.created_at == created
+
+
+def test_friend_response_maps_fields() -> None:
+    friend_user = UserBasicInfo(id="user-2", username="bob", avatar_url=None)
+    request_id = uuid4()
+    created = datetime(2026, 1, 15, 10, 30, 0)
+    accepted = datetime(2026, 1, 16, 12, 0, 0)
+
+    response = FriendResponse(
+        id=request_id,
+        friend=friend_user,
+        status="accepted",
+        created_at=created,
+        accepted_at=accepted,
+    )
+
+    assert response.id == request_id
+    assert response.friend.username == "bob"
+    assert response.status == "accepted"
+    assert response.accepted_at == accepted
+
+
+def test_friend_response_accepted_at_optional() -> None:
+    friend_user = UserBasicInfo(id="user-2", username="bob", avatar_url=None)
+    request_id = uuid4()
+    created = datetime(2026, 1, 15, 10, 30, 0)
+
+    response = FriendResponse(
+        id=request_id,
+        friend=friend_user,
+        status="pending",
+        created_at=created,
+        accepted_at=None,
+    )
+
+    assert response.accepted_at is None
+
+
+def test_friend_request_action_no_fields() -> None:
+    action = FriendRequestAction()
+    assert action.model_dump() == {}