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>

CHANGELOG.md

@@ -2,6 +2,27 @@
 
 All notable changes to Armature are documented here.
 
+## v0.7.3 — Extension Shell Migration
+
+**Shell Topbar Migration**
+- Migrated Chat, Notes, and Schedules from legacy `sw.shell.Topbar` component to the v0.7.0 shell topbar contract (`sw.shell.topbar.setTitle/setSlot`)
+- Eliminated double topbar (shell-injected + surface-owned) on all three extension surfaces
+- Chat: reactive slot updates for thread title + People button when conversation changes
+- Notes: slot content for + New Note, Import .md, and Graph toggle buttons
+- Schedules: reactive slot with schedule count and + New Schedule button; removed legacy fallback branch
+
+**Runner Test Updates**
+- Added `shell-topbar` test suite to chat-runner, notes-runner, and schedules-runner
+- Tests fetch surface JS and assert: no legacy `sw.shell.Topbar` reference, uses `sw.shell.topbar.setTitle/setSlot` API
+- 6 new tests across 3 runners
+
+**Package Versions**
+- Chat surface v0.3.0, Notes surface v0.9.0, Schedules surface v0.2.0
+- Chat runner v0.2.0, Notes runner v0.2.0, Schedules runner v0.2.0
+
+**Roadmap**
+- Headless E2E automation moved to v0.7.5 (independent from shell migration)
+
 ## v0.7.1 — Surface Runner Framework
 
 **`sw.testing` SDK Module**