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

web/src/chat/types.ts

@@ -6,10 +6,18 @@ export interface Chat {
   id: number;
   type: ChatType;
   title: string | null;
+  handle?: string | null;
+  description?: string | null;
+  is_public?: boolean;
+  is_saved?: boolean;
   pinned_message_id?: number | null;
   created_at: string;
 }
 
+export interface DiscoverChat extends Chat {
+  is_member: boolean;
+}
+
 export interface Message {
   id: number;
   chat_id: number;