Carry conversations into new sessions with a visible summary

- Bots get continue_in_new_session: the bot writes a title and summary,
  the session closes for good (read-only) and the new one opens with the
  summary as a "Carried over from the last session" message that links
  back to the old session.
- Continue in new session (conversation menu, sessions modal) and the
  automatic rollover at the session length do the same; New session now
  starts a fresh, unlinked session.
- Session length is an app setting in Settings > General.
- ?session_id= opens a session; a carried-over one shows a bar linking to
  where the conversation went on instead of the composer.
- The thread can open the previous session above the current one (shown
  only, never in the prompt), and replies get search_past_sessions and
  read_past_session.
- Sessions are named from their opening messages, not their latest, and
  a carried summary is labelled as the earlier session's.

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

src/dict/bot-dict.ts

@@ -116,6 +116,13 @@ export const BotSystemPromptAppendSettingKey = "bot_system_prompt_append";
  */
 export const BotReplyMaxToolStepsSettingKey = "bot_reply_max_tool_steps";
 
+/**
+ * The `app_settings` key holding how many messages a session takes before
+ * the next user message starts a new one. Unset means
+ * `AppData.BotSessionMaxMessages`.
+ */
+export const BotSessionMaxMessagesSettingKey = "bot_session_max_messages";
+
 /**
  * A bot's face is its status. There are no badges or spinners.
  */