Feat v0.7.3 extension shell migration

Migrate Chat, Notes, and Schedules from legacy sw.shell.Topbar to the
v0.7.0 shell topbar contract (sw.shell.topbar.setTitle/setSlot),
eliminating double topbars on all extension surfaces.

- Chat v0.3.0: reactive slot for thread title + People button
- Notes v0.9.0: slot for New/Import/Graph buttons
- Schedules v0.2.0: reactive slot for count + New button
- 6 new shell-topbar runner tests (2 per surface)
- Headless E2E deferred to v0.7.5

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/notes-runner/js/main.js

@@ -36,7 +36,8 @@
   var modules = [
     'notes-crud.js',
     'folders.js',
-    'tags-search.js'
+    'tags-search.js',
+    'shell-topbar.js'
   ];
 
   var loaded = 0;

packages/notes-runner/js/shell-topbar.js

@@ -0,0 +1,31 @@
+/**
+ * Notes Runner — notes/shell-topbar suite
+ *
+ * Validates the Notes surface uses the v0.7.0 shell topbar contract
+ * and does not render the legacy sw.shell.Topbar component.
+ */
+(function () {
+  'use strict';
+
+  sw.testing.suite('notes/shell-topbar', async function (s) {
+
+    s.test('surface JS does not reference legacy Topbar', async function (t) {
+      var base = window.__BASE__ || '';
+      var resp = await fetch(base + '/surfaces/notes/js/main.js');
+      t.assert.eq(resp.status, 200, 'fetched notes main.js');
+      var src = await resp.text();
+      var hasLegacy = src.indexOf('sw.shell.Topbar') !== -1;
+      t.assert.ok(!hasLegacy, 'no sw.shell.Topbar reference (uses shell topbar API)');
+    });
+
+    s.test('surface JS uses shell topbar API', async function (t) {
+      var base = window.__BASE__ || '';
+      var resp = await fetch(base + '/surfaces/notes/js/main.js');
+      var src = await resp.text();
+      var usesAPI = src.indexOf('sw.shell.topbar.setTitle') !== -1
+                 || src.indexOf('sw.shell.topbar.setSlot') !== -1;
+      t.assert.ok(usesAPI, 'uses sw.shell.topbar.setTitle or setSlot');
+    });
+
+  });
+})();