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/messages/router.py

@@ -4,7 +4,15 @@ from sqlalchemy.ext.asyncio import AsyncSession
 from app.auth.service import get_current_user
 from app.database.session import get_db
 from app.messages.schemas import MessageCreateRequest, MessageForwardRequest, MessageRead, MessageStatusUpdateRequest, MessageUpdateRequest
-from app.messages.service import create_chat_message, delete_message, forward_message, get_messages, search_messages, update_message
+from app.messages.service import (
+    create_chat_message,
+    delete_message,
+    delete_message_for_all,
+    forward_message,
+    get_messages,
+    search_messages,
+    update_message,
+)
 from app.realtime.schemas import MessageStatusPayload
 from app.realtime.service import realtime_gateway
 from app.users.models import User
@@ -62,9 +70,13 @@ async def edit_message(
 @router.delete("/{message_id}", status_code=status.HTTP_204_NO_CONTENT)
 async def remove_message(
     message_id: int,
+    for_all: bool = False,
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user),
 ) -> None:
+    if for_all:
+        await delete_message_for_all(db, message_id=message_id, user_id=current_user.id)
+        return
     await delete_message(db, message_id=message_id, user_id=current_user.id)