Name sessions opened by handed-off work, and hide empty ones from activity

A session the coordinator's delegation, a routine or a hook opened has
no user message and no reply, so it was never named and showed as
"Untitled conversation". Tasks now name their session too, and a session
with no user message is named from the bot's own messages. Until a
session is named, Latest activity shows what it opened with, and
sessions with no messages are left out of it.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/types/index.ts

@@ -275,6 +275,10 @@ export type WorkspaceWithActivity = BUN_SQLITE_COBBLE_WORKSPACES & {
  */
 export type WorkspaceActivityItem = BUN_SQLITE_COBBLE_BOT_SESSIONS & {
     message_count: number;
+    /**
+     * What the session opened with, shown while it has no title yet.
+     */
+    first_message_text?: string | null;
     last_message_text?: string | null;
     bot_name?: string | null;
     bot_image_media_id?: number | null;