fix: make session ordering follow activity lifecycle

Session lists now promote a conversation when it starts working and again when it settles, instead of reacting to every streaming timestamp update. This keeps ordering responsive without bringing back the sidebar churn removed by the recent performance work.

Apply the same user-visible order across Recent, project and worktree groups, session switchers, mobile navigation, widgets, the command palette, and the desktop tray. Preserve pinned priority, freeze timestamp fallback ordering, and keep child-session activity scoped to siblings under the same parent so it never moves the root conversation.

Seed reconnect snapshots without synthetic jumps, clear ephemeral ranks on deletion and runtime changes, and cover lifecycle transitions, mixed root/child trees, metadata-only updates, and project-group ordering with regression tests.

packages/ui/src/stores/DOCUMENTATION.md

@@ -52,6 +52,8 @@ These stores coordinate persistent project/session metadata across multiple view
 
 `useGlobalSessionsStore.ts` owns cold/global active and archived session coverage, including `sessionsByDirectory`. It is complementary to directory child stores: it is not the source of live busy/retry status or session messages.
 
+User-visible session ordering is also not owned by the global cache array order. `sync/session-ordering.ts` combines lifecycle rank with timestamp fallbacks, and session surfaces must use that shared comparator instead of independently sorting global sessions by `time.updated`.
+
 Global refresh rules:
 
 - Per-directory refresh is bounded to two requests across callers and prioritizes the current directory.