feat(web): name the agent-preset surface "Agent 预设" in Chinese

The Chinese copy was mixed: the nav read 智能体 while every other string kept
`preset` untranslated (本会话的 agent preset, 新建 preset, preset 名称).
It is now one register throughout — Agent stays, preset becomes 预设, the
standard Chinese UI word for a named, switchable configuration bundle, which
is what a preset is when a session picks one.

UI copy only. The docs keep `agent preset` as the technical term for the
composition and the `agent-presets` plugin.

packages/client/ui-agent-preset/tests/apply.spec.ts

@@ -91,7 +91,7 @@ describe('ui-agent-preset apply', () => {
     expect(section.component).toBe(AgentPresetSection)
     expect(section.options).toMatchObject({ id: 'agent-presets', order: 20 })
     // The nav label is a locale-following thunk; owners resolve it at read time.
-    expect(resolveSlotLabel(section.options.label)).toBe('智能体')
+    expect(resolveSlotLabel(section.options.label)).toBe('Agent 预设')
   })
 
   it('registers into a declaration that arrives after apply', async () => {