fix(SearchPalette): return null while closed

The Overlay refactor dropped the early return, so the fixed-inset backdrop
stayed mounted permanently: the palette covered the page and swallowed
every click. Restore the guard and cover it with tests.

tests/overlay.test.tsx

@@ -3,6 +3,7 @@ import { useState } from 'react'
 import { describe, expect, it } from 'vitest'
 import { Dialog, DialogContent, DialogDescription, DialogTitle } from '../src/components/ui/Dialog'
 import { Sheet, SheetClose, SheetContent, SheetTitle } from '../src/components/ui/Sheet'
+import { SearchPalette } from '../src/components/SearchPalette'
 
 describe('Dialog (Overlay primitive)', () => {
   it('renders a modal dialog with the panel focused when open', () => {
@@ -168,3 +169,41 @@ describe('Sheet (Overlay skin)', () => {
     expect(last).toHaveFocus()
   })
 })
+
+describe('SearchPalette (Overlay behavior)', () => {
+  it('renders nothing while closed and no backdrop is left over the page', () => {
+    const { rerender } = render(
+      <SearchPalette isOpen={false} onClose={() => {}} onSelect={() => {}} />,
+    )
+    expect(screen.queryByRole('dialog')).toBeNull()
+    expect(document.querySelector('.search-palette-backdrop')).toBeNull()
+    expect(document.body.style.overflow).toBe('')
+
+    rerender(<SearchPalette isOpen onClose={() => {}} onSelect={() => {}} />)
+    expect(screen.getByRole('dialog')).toHaveClass('search-palette-modal')
+  })
+
+  it('closes on Escape / backdrop click and unlocks body scroll', () => {
+    function Controlled() {
+      const [open, setOpen] = useState(true)
+      return (
+        <>
+          <button onClick={() => setOpen(true)}>Open</button>
+          <SearchPalette isOpen={open} onClose={() => setOpen(false)} onSelect={() => {}} />
+        </>
+      )
+    }
+    const { container } = render(<Controlled />)
+    expect(document.body.style.overflow).toBe('hidden')
+
+    fireEvent.keyDown(window, { key: 'Escape' })
+    expect(screen.queryByRole('dialog')).toBeNull()
+    expect(document.body.style.overflow).toBe('')
+
+    fireEvent.click(screen.getByRole('button', { name: 'Open' }))
+    expect(screen.getByRole('dialog')).toBeInTheDocument()
+    fireEvent.click(container.querySelector('.search-palette-backdrop')!)
+    expect(screen.queryByRole('dialog')).toBeNull()
+    expect(document.body.style.overflow).toBe('')
+  })
+})