feat(core): clear saved chat and add message deletion scopes

backend:

- add message_hidden table for per-user message hiding

- support DELETE /messages/{id}?for_all=true|false

- implement delete-for-me vs delete-for-all logic by chat type/permissions

- add POST /chats/{chat_id}/clear and route saved chat deletion to clear

web:

- saved messages action changed from delete to clear

- message context menu now supports delete modal: for me / for everyone

- add local store helpers removeMessage/clearChatMessages

- include realtime stability improvements and app error boundary

app/chats/service.py

@@ -5,7 +5,13 @@ 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, ChatRead, ChatTitleUpdateRequest
-from app.messages.repository import get_message_by_id
+from app.messages.repository import (
+    delete_messages_in_chat,
+    get_hidden_message,
+    get_message_by_id,
+    hide_message_for_user,
+    list_chat_message_ids,
+)
 from app.users.repository import get_user_by_id
 
 
@@ -349,6 +355,9 @@ 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)
+    if chat.is_saved:
+        await clear_chat_for_user(db, chat_id=chat_id, user_id=user_id)
+        return
     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}:
@@ -358,3 +367,18 @@ async def delete_chat_for_user(db: AsyncSession, *, chat_id: int, user_id: int,
         return
     await repository.delete_chat_member(db, membership)
     await db.commit()
+
+
+async def clear_chat_for_user(db: AsyncSession, *, chat_id: int, user_id: int) -> None:
+    chat, _membership = await _get_chat_and_membership(db, chat_id=chat_id, user_id=user_id)
+    if chat.is_saved:
+        await delete_messages_in_chat(db, chat_id=chat_id)
+        await db.commit()
+        return
+    message_ids = await list_chat_message_ids(db, chat_id=chat_id)
+    for message_id in message_ids:
+        already_hidden = await get_hidden_message(db, message_id=message_id, user_id=user_id)
+        if already_hidden:
+            continue
+        await hide_message_for_user(db, message_id=message_id, user_id=user_id)
+    await db.commit()