refactor(gui): session titles ride the generic projection pair; title-snapshot map retired

The manager's titleSnapshots Map and its session/title frame consumption
dissolve into resident per-session ProjectionValueStores (create-on-demand,
outliving instantiation — the same role the snapshot map played): a
session/projection frame lands whether or not the Session exists, list rows
read the store's 'title' key, subscribed baselines truncate phantom rows, and
session-removed drops the store. The fixture converts to the host parallel:
a projections block on the tail page (title + todos units), push frames on
unit-advancing events, and a post-subscribe projection baseline replacing the
bespoke title control frame.

packages/client/runtime/tests/sessions-service.spec.ts

@@ -47,7 +47,7 @@ describe('list store projection', () => {
     const b = bench()
     b.svc.handleMuxEnvelope({
       rpcId: 'title' as never,
-      payload: { type: 'session/title', sessionId: sid('s1'), title: 'Durable title', eventSeq: 2, updatedAt: 3 },
+      payload: { type: 'session/projection', sessionId: sid('s1'), key: 'title', value: 'Durable title', seq: 2 } as never,
     })
     await feedList(b, [
       { id: 's1', cwd: '/home/u/proj-a/' },