feat: add user display profiles and fix web context menu UX

backend:

- add required user name and optional bio fields

- extend auth/register and user schemas/services with name/bio

- add alembic migration 0006 with safe backfill name=username

- compute per-user chat display_title for private chats

- keep Saved Messages delete-for-all protections

web:

- registration now includes name

- add profile edit modal (name/username/bio/avatar url)

- show private chat names via display_title

- fix context menus to open near cursor with viewport clamping

- stabilize +/close floating button to remove visual jump

app/chats/service.py

@@ -4,11 +4,42 @@ from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.chats import repository
 from app.chats.models import Chat, ChatMember, ChatMemberRole, ChatType
-from app.chats.schemas import ChatCreateRequest, ChatDeleteRequest, ChatDiscoverRead, ChatPinMessageRequest, ChatTitleUpdateRequest
+from app.chats.schemas import ChatCreateRequest, ChatDeleteRequest, ChatDiscoverRead, ChatPinMessageRequest, ChatRead, ChatTitleUpdateRequest
 from app.messages.repository import get_message_by_id
 from app.users.repository import get_user_by_id
 
 
+async def serialize_chat_for_user(db: AsyncSession, *, user_id: int, chat: Chat) -> ChatRead:
+    display_title = chat.title
+    if chat.is_saved:
+        display_title = "Saved Messages"
+    elif chat.type == ChatType.PRIVATE:
+        counterpart_id = await repository.get_private_counterpart_user_id(db, chat_id=chat.id, user_id=user_id)
+        if counterpart_id:
+            counterpart = await get_user_by_id(db, counterpart_id)
+            if counterpart:
+                display_title = counterpart.name or counterpart.username
+
+    return ChatRead.model_validate(
+        {
+            "id": chat.id,
+            "type": chat.type,
+            "title": chat.title,
+            "display_title": display_title,
+            "handle": chat.handle,
+            "description": chat.description,
+            "is_public": chat.is_public,
+            "is_saved": chat.is_saved,
+            "pinned_message_id": chat.pinned_message_id,
+            "created_at": chat.created_at,
+        }
+    )
+
+
+async def serialize_chats_for_user(db: AsyncSession, *, user_id: int, chats: list[Chat]) -> list[ChatRead]:
+    return [await serialize_chat_for_user(db, user_id=user_id, chat=chat) for chat in chats]
+
+
 async def create_chat_for_user(db: AsyncSession, *, creator_id: int, payload: ChatCreateRequest) -> Chat:
     member_ids = list(dict.fromkeys(payload.member_ids))
     member_ids = [member_id for member_id in member_ids if member_id != creator_id]
@@ -318,7 +349,7 @@ async def join_public_chat_for_user(db: AsyncSession, *, chat_id: int, user_id:
 
 async def delete_chat_for_user(db: AsyncSession, *, chat_id: int, user_id: int, payload: ChatDeleteRequest) -> None:
     chat, membership = await _get_chat_and_membership(db, chat_id=chat_id, user_id=user_id)
-    delete_for_all = payload.for_all or chat.type == ChatType.CHANNEL
+    delete_for_all = (payload.for_all and not chat.is_saved) or chat.type == ChatType.CHANNEL
     if delete_for_all:
         if chat.type in {ChatType.GROUP, ChatType.CHANNEL} and membership.role not in {ChatMemberRole.OWNER, ChatMemberRole.ADMIN}:
             raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail="Insufficient permissions")