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/repository.py

@@ -3,7 +3,7 @@ from datetime import datetime, timezone
 from sqlalchemy import and_, func, or_, select
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from app.users.models import BlockedUser, User
+from app.users.models import BlockedUser, User, UserContact
 
 
 async def create_user(db: AsyncSession, *, email: str, name: str, username: str, password_hash: str) -> User:
@@ -107,3 +107,40 @@ async def list_blocked_users(db: AsyncSession, *, user_id: int) -> list[User]:
     )
     result = await db.execute(stmt)
     return list(result.scalars().all())
+
+
+async def add_contact(db: AsyncSession, *, user_id: int, contact_user_id: int) -> UserContact:
+    existing = await get_contact_relation(db, user_id=user_id, contact_user_id=contact_user_id)
+    if existing:
+        return existing
+    relation = UserContact(user_id=user_id, contact_user_id=contact_user_id)
+    db.add(relation)
+    await db.flush()
+    return relation
+
+
+async def remove_contact(db: AsyncSession, *, user_id: int, contact_user_id: int) -> None:
+    relation = await get_contact_relation(db, user_id=user_id, contact_user_id=contact_user_id)
+    if relation:
+        await db.delete(relation)
+
+
+async def get_contact_relation(db: AsyncSession, *, user_id: int, contact_user_id: int) -> UserContact | None:
+    result = await db.execute(
+        select(UserContact).where(
+            UserContact.user_id == user_id,
+            UserContact.contact_user_id == contact_user_id,
+        )
+    )
+    return result.scalar_one_or_none()
+
+
+async def list_contacts(db: AsyncSession, *, user_id: int) -> list[User]:
+    stmt = (
+        select(User)
+        .join(UserContact, UserContact.contact_user_id == User.id)
+        .where(UserContact.user_id == user_id)
+        .order_by(User.username.asc())
+    )
+    result = await db.execute(stmt)
+    return list(result.scalars().all())