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/pages/admin/settings/general/index.tsx

@@ -5,6 +5,7 @@ import InstallNameSection from "./(sections)/install-name-section";
 import NotificationsSection from "./(sections)/notifications-section";
 import PromptSection from "./(sections)/prompt-section";
 import RunLimitsSection from "./(sections)/run-limits-section";
+import SessionLengthSection from "./(sections)/session-length-section";
 import SkillLimitsSection from "./(sections)/skill-limits-section";
 import StorageSection from "./(sections)/storage-section";
 import VersionSection from "./(sections)/version-section";
@@ -23,6 +24,7 @@ export default function AdminSettingsGeneralPage() {
             <NotificationsSection />
             <PromptSection />
             <RunLimitsSection />
+            <SessionLengthSection />
             <SkillLimitsSection />
             <HookCallRetentionSection />
             <StorageSection />