Merge branch 'stack/agent-profiles-5-web-ui' into stack/agent-profiles-8-authoring

The composer's preset seat stays removed here — this layer moved it to the
hero chip and the session-header action — so only the model seat takes the
`modelSeatLocked` narrowing master introduced.

Conflicts:
	apps/web/tests/snapshots/*/*.expected.md
	packages/client/connection/README.md
	packages/client/connection/README.zh.md
	packages/client/ui-conversation/src/client/skeleton/InputBar.tsx
	packages/host/apiproxy/src/fetch/client.ts

apps/web/tests/snapshots/lifecycle-chrome/plan-active.expected.md

@@ -20,7 +20,7 @@
 - button "Settings":
   - img
   - text: Settings
-- text: Let's start building Preview
+- text: Into the Unknown Preview
 - button "Choose workspace":
   - img
   - text: workspace
@@ -34,8 +34,8 @@
   - img
 - 'button "Access mode, current: Workspace Write"': Workspace Write
 - button "Plan mode on, press to turn off": Plan
-- button "Select model":
-  - text: Select model
+- button "Select model, current DeepSeek-V4-Flash":
+  - text: DeepSeek-V4-Flash
   - img
 - button "Send message" [disabled]
 - text: Details