feat(contacts): add contacts module with backend APIs and web tab

- add user_contacts table and migration

- expose /users/contacts list/add/remove endpoints

- add Contacts tab in chat list with add/remove actions

app/users/router.py

@@ -6,10 +6,14 @@ from app.database.session import get_db
 from app.users.models import User
 from app.users.schemas import UserProfileUpdate, UserRead, UserSearchRead
 from app.users.service import (
+    add_contact,
     block_user,
     get_user_by_id,
     get_user_by_username,
     list_blocked_users,
+    list_contacts,
+    has_block_relation_between_users,
+    remove_contact,
     search_users_by_username,
     unblock_user,
     update_user_profile,
@@ -72,6 +76,42 @@ async def read_blocked_users(
     return await list_blocked_users(db, user_id=current_user.id)
 
 
+@router.get("/contacts", response_model=list[UserSearchRead])
+async def read_contacts(
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+) -> list[UserSearchRead]:
+    return await list_contacts(db, user_id=current_user.id)
+
+
+@router.post("/{user_id}/contacts", status_code=status.HTTP_204_NO_CONTENT)
+async def add_contact_endpoint(
+    user_id: int,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+) -> None:
+    if user_id == current_user.id:
+        raise HTTPException(status_code=status.HTTP_422_UNPROCESSABLE_ENTITY, detail="Cannot add yourself")
+    target = await get_user_by_id(db, user_id)
+    if not target:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="User not found")
+    is_blocked = await has_block_relation_between_users(db, user_a_id=current_user.id, user_b_id=user_id)
+    if is_blocked:
+        raise HTTPException(status_code=status.HTTP_409_CONFLICT, detail="Cannot add contact while blocked")
+    await add_contact(db, user_id=current_user.id, contact_user_id=user_id)
+
+
+@router.delete("/{user_id}/contacts", status_code=status.HTTP_204_NO_CONTENT)
+async def remove_contact_endpoint(
+    user_id: int,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+) -> None:
+    if user_id == current_user.id:
+        return
+    await remove_contact(db, user_id=current_user.id, contact_user_id=user_id)
+
+
 @router.post("/{user_id}/block", status_code=status.HTTP_204_NO_CONTENT)
 async def block_user_endpoint(
     user_id: int,