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/models.py

@@ -2,7 +2,7 @@ from datetime import datetime
 from enum import Enum
 from typing import TYPE_CHECKING
 
-from sqlalchemy import DateTime, Enum as SAEnum, ForeignKey, String, UniqueConstraint, func
+from sqlalchemy import Boolean, DateTime, Enum as SAEnum, ForeignKey, String, UniqueConstraint, func
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from app.database.base import Base
@@ -30,6 +30,10 @@ class Chat(Base):
     id: Mapped[int] = mapped_column(primary_key=True, index=True)
     type: Mapped[ChatType] = mapped_column(SAEnum(ChatType), nullable=False, index=True)
     title: Mapped[str | None] = mapped_column(String(255), nullable=True)
+    handle: Mapped[str | None] = mapped_column(String(64), nullable=True, unique=True, index=True)
+    description: Mapped[str | None] = mapped_column(String(512), nullable=True)
+    is_public: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False, server_default="false")
+    is_saved: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False, server_default="false")
     pinned_message_id: Mapped[int | None] = mapped_column(ForeignKey("messages.id", ondelete="SET NULL"), nullable=True, index=True)
     created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now(), nullable=False)