feat: add saved messages, public chat discovery/join, and chat delete options

- add Saved Messages system chat with dedicated API

- add public group/channel metadata and discover/join endpoints

- add chat delete flow with for_all option and channel-wide delete

- switch message actions to context menu and improve reply/forward visuals

- improve microphone permission handling for voice recording

app/chats/repository.py

@@ -12,6 +12,29 @@ async def create_chat(db: AsyncSession, *, chat_type: ChatType, title: str | Non
     return chat
 
 
+async def create_chat_with_meta(
+    db: AsyncSession,
+    *,
+    chat_type: ChatType,
+    title: str | None,
+    handle: str | None,
+    description: str | None,
+    is_public: bool,
+    is_saved: bool = False,
+) -> Chat:
+    chat = Chat(
+        type=chat_type,
+        title=title,
+        handle=handle,
+        description=description,
+        is_public=is_public,
+        is_saved=is_saved,
+    )
+    db.add(chat)
+    await db.flush()
+    return chat
+
+
 async def add_chat_member(db: AsyncSession, *, chat_id: int, user_id: int, role: ChatMemberRole) -> ChatMember:
     member = ChatMember(chat_id=chat_id, user_id=user_id, role=role)
     db.add(member)
@@ -61,6 +84,11 @@ async def get_chat_by_id(db: AsyncSession, chat_id: int) -> Chat | None:
     return result.scalar_one_or_none()
 
 
+async def get_chat_by_handle(db: AsyncSession, handle: str) -> Chat | None:
+    result = await db.execute(select(Chat).where(Chat.handle == handle))
+    return result.scalar_one_or_none()
+
+
 async def get_chat_member(db: AsyncSession, *, chat_id: int, user_id: int) -> ChatMember | None:
     result = await db.execute(
         select(ChatMember).where(
@@ -83,6 +111,38 @@ async def list_user_chat_ids(db: AsyncSession, *, user_id: int) -> list[int]:
     return list(result.scalars().all())
 
 
+async def find_saved_chat_for_user(db: AsyncSession, *, user_id: int) -> Chat | None:
+    stmt = (
+        select(Chat)
+        .join(ChatMember, ChatMember.chat_id == Chat.id)
+        .where(ChatMember.user_id == user_id, Chat.is_saved.is_(True))
+        .limit(1)
+    )
+    result = await db.execute(stmt)
+    return result.scalar_one_or_none()
+
+
+async def discover_public_chats(
+    db: AsyncSession,
+    *,
+    user_id: int,
+    query: str | None = None,
+    limit: int = 30,
+) -> list[tuple[Chat, bool]]:
+    q = select(Chat).where(Chat.is_public.is_(True), Chat.type.in_([ChatType.GROUP, ChatType.CHANNEL]), Chat.is_saved.is_(False))
+    if query and query.strip():
+        like = f"%{query.strip()}%"
+        q = q.where(or_(Chat.title.ilike(like), Chat.handle.ilike(like), Chat.description.ilike(like)))
+    q = q.order_by(Chat.id.desc()).limit(limit)
+    chats = list((await db.execute(q)).scalars().all())
+    if not chats:
+        return []
+    chat_ids = [c.id for c in chats]
+    m_stmt = select(ChatMember.chat_id).where(ChatMember.user_id == user_id, ChatMember.chat_id.in_(chat_ids))
+    memberships = set((await db.execute(m_stmt)).scalars().all())
+    return [(chat, chat.id in memberships) for chat in chats]
+
+
 async def find_private_chat_between_users(db: AsyncSession, *, user_a_id: int, user_b_id: int) -> Chat | None:
     cm_a = aliased(ChatMember)
     cm_b = aliased(ChatMember)