feat: add search APIs and telegram-like chats sidebar flow

- implement chat query filtering and message search endpoints

- add db indexes for search fields

- activate chats search input in web

- replace inline create panel with floating TG-style action menu

app/messages/repository.py

@@ -1,6 +1,7 @@
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
+from app.chats.models import ChatMember
 from app.messages.models import Message, MessageIdempotencyKey, MessageReceipt, MessageType
 
 
@@ -76,6 +77,31 @@ async def list_chat_messages(
     return list(result.scalars().all())
 
 
+async def search_messages(
+    db: AsyncSession,
+    *,
+    user_id: int,
+    query: str,
+    chat_id: int | None = None,
+    limit: int = 50,
+) -> list[Message]:
+    stmt = (
+        select(Message)
+        .join(ChatMember, ChatMember.chat_id == Message.chat_id)
+        .where(
+            ChatMember.user_id == user_id,
+            Message.text.is_not(None),
+            Message.text.ilike(f"%{query.strip()}%"),
+        )
+        .order_by(Message.id.desc())
+        .limit(limit)
+    )
+    if chat_id is not None:
+        stmt = stmt.where(Message.chat_id == chat_id)
+    result = await db.execute(stmt)
+    return list(result.scalars().all())
+
+
 async def delete_message(db: AsyncSession, message: Message) -> None:
     await db.delete(message)