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

packages/host/apiproxy/tests/client-handler.spec.ts

@@ -46,6 +46,7 @@ function scriptedApi(overrides: {
       }),
       models: r => ok(r, {
         current: { provider: 'deepseek-official', model: 'deepseek-v4-flash' },
+        routable: true,
         groups: [],
         failures: [],
       }),