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/api-proxy-agent-preset.spec.ts

@@ -107,7 +107,11 @@ async function harness(presets?: readonly string[]) {
     },
   }
   ctx.agents.setFactory(factory)
-  const api = createApiProxy(ctx, { provider: 'test', model: 'test-model', cwd, workspaceRoot: cwd })
+  const api = createApiProxy(ctx, {
+    defaultTarget: () => ({ provider: 'test', model: 'test-model' }),
+    cwd,
+    workspaceRoot: cwd,
+  })
   return { api, ctx, cwd }
 }