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/onboarding-deepseek-config/models.expected.md

@@ -28,12 +28,6 @@
         - text: 自定义设置 API 地址
         - textbox "API 地址":
           - /placeholder: https://api.deepseek.com
-        - text: 推理强度
-        - combobox "推理强度":
-          - option "默认" [selected]
-          - option "off"
-          - option "high"
-          - option "max"
         - region "模型目录":
           - text: 模型目录 已自定义模型目录
           - button "恢复默认模型"