fix(chat): repair Arco migration fallout in the chat page

The Phase 006 walkthrough surfaced four issues the automated checks could
not see. Dead naive-ui class names left behind by the migration stopped
matching, tooltips that carried their label as trailing default-slot text
leaked that text into the flex row, the workspace panel squeezed the chat
column until the input toolbar wrapped, and the Escape fallback still
looked for naive-ui's modal mask.

Tooltips now pass their label through the content prop, the tool panel
reserves a minimum width for the chat column, and Escape finds the visible
Arco modal and clicks its close button.

tests/client/session-search.test.ts

@@ -209,4 +209,38 @@ describe('keyboard shortcut', () => {
 
     expect(useSessionSearch().sessionSearchOpen.value).toBe(true)
   })
+
+  // The chat page dialogs all moved to Arco in Phase 006, so the Esc fallback
+  // must look for Arco's close button, not naive-ui's.
+  it('closes an open Arco modal on Escape, and ignores naive-ui markup', () => {
+    const close = vi.fn()
+    const modal = document.createElement('div')
+    modal.className = 'arco-modal'
+    const closeBtn = document.createElement('div')
+    closeBtn.className = 'arco-modal-close-btn'
+    closeBtn.addEventListener('click', close)
+    modal.appendChild(closeBtn)
+    document.body.appendChild(modal)
+
+    const legacyModal = document.createElement('div')
+    legacyModal.className = 'n-modal n-modal-mask'
+    document.body.appendChild(legacyModal)
+
+    const Dummy = defineComponent({
+      setup() {
+        useKeyboard()
+        return () => h('div')
+      },
+    })
+    const wrapper = mount(Dummy)
+    // jsdom reports offsetParent as null, so make the modal look visible.
+    Object.defineProperty(modal, 'offsetParent', { value: document.body })
+
+    window.dispatchEvent(new KeyboardEvent('keydown', { key: 'Escape' }))
+    expect(close).toHaveBeenCalled()
+
+    wrapper.unmount()
+    modal.remove()
+    legacyModal.remove()
+  })
 })