fix: float browser preview zoom controls (#952)

Move the preview zoom control out of the address toolbar and into a bottom-right floating control area inside the browser preview stage. Keep the native WebContentsView bounds clear of the control strip so the DOM control remains interactive on high-DPI Windows displays.

Tested: cd desktop && bun run test -- src/components/browser/BrowserSurface.test.tsx

Tested: cd desktop && bun run lint

Tested: cd desktop && bun run build

Not-tested: Windows high-DPI real-device smoke.

Confidence: medium

Scope-risk: narrow

desktop/src/components/browser/BrowserSurface.test.tsx

@@ -182,16 +182,19 @@ describe('BrowserSurface', () => {
     expect(bridge.message).toHaveBeenLastCalledWith({ v: 1, type: 'exit-picker' })
   })
 
-  it('renders toolbar preview zoom controls that update the native preview zoom', async () => {
+  it('renders floating preview zoom controls that update the native preview zoom', async () => {
     useBrowserPanelStore.getState().open('s1', 'http://localhost:5173/')
     useBrowserPanelStore.getState().setReady('s1')
     render(<BrowserSurface sessionId="s1" />)
 
     const controls = screen.getByTestId('browser-zoom-controls')
     const actions = screen.getByTestId('browser-toolbar-actions')
+    const floatingControls = screen.getByTestId('browser-preview-floating-controls')
     expect(controls).toHaveTextContent('100%')
-    expect(actions).toContainElement(controls)
-    expect(controls.compareDocumentPosition(screen.getByTestId('preview-host')) & Node.DOCUMENT_POSITION_FOLLOWING).toBeTruthy()
+    expect(actions).not.toContainElement(controls)
+    expect(floatingControls).toContainElement(controls)
+    expect(screen.getByTestId('browser-preview-stage')).toContainElement(floatingControls)
+    expect(screen.getByTestId('preview-host').compareDocumentPosition(floatingControls) & Node.DOCUMENT_POSITION_FOLLOWING).toBeTruthy()
 
     fireEvent.click(screen.getByLabelText('缩小预览'))
     expect(useBrowserPanelStore.getState().bySession['s1']!.zoom).toBe(0.9)

desktop/src/components/browser/BrowserSurface.tsx

@@ -208,7 +208,7 @@ export function BrowserSurface({ sessionId }: { sessionId: string }) {
   }
 
   const zoomButtonClass = [
-    'inline-flex h-7 w-7 items-center justify-center rounded-full transition-colors',
+    'inline-flex h-8 w-8 items-center justify-center rounded-full transition-colors',
     'text-[var(--color-text-secondary)] hover:bg-[var(--color-surface-container-low)] hover:text-[var(--color-text-primary)]',
     'disabled:cursor-default disabled:opacity-35 disabled:hover:bg-transparent disabled:hover:text-[var(--color-text-secondary)]',
     'focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-[var(--color-brand)]',
@@ -217,7 +217,9 @@ export function BrowserSurface({ sessionId }: { sessionId: string }) {
   const zoomControls = (
     <div
       data-testid="browser-zoom-controls"
-      className="inline-flex h-8 shrink-0 items-center gap-1 rounded-full border border-[var(--color-border)] bg-[var(--color-surface)] px-1 shadow-sm"
+      role="group"
+      aria-label="预览缩放控制"
+      className="inline-flex h-10 shrink-0 items-center gap-1 rounded-full border border-[var(--color-border)] bg-[var(--color-surface)] px-1.5 shadow-lg"
     >
       <button
         aria-label="缩小预览"
@@ -285,7 +287,6 @@ export function BrowserSurface({ sessionId }: { sessionId: string }) {
       >
         <MousePointer2 size={16} />
       </button>
-      {zoomControls}
     </>
   )
 
@@ -317,12 +318,23 @@ export function BrowserSurface({ sessionId }: { sessionId: string }) {
         rightActions={previewActions}
       />
       <div className="flex min-h-0 flex-1 flex-col bg-[var(--color-surface)]">
-        <div ref={hostRef} className="relative min-h-0 flex-1 overflow-hidden" data-testid="preview-host">
-          {session.loading && (
-            <div className="pointer-events-none absolute inset-0 flex items-center justify-center bg-[var(--color-surface)] text-[var(--color-text-tertiary)]">
-              <Loader2 size={18} className="animate-spin" aria-label="加载中" />
+        <div className="relative min-h-0 flex-1 overflow-hidden" data-testid="browser-preview-stage">
+          {/* WebContentsView renders above DOM, so keep the floating controls outside its bounds. */}
+          <div ref={hostRef} className="absolute inset-x-0 top-0 bottom-12 overflow-hidden" data-testid="preview-host">
+            {session.loading && (
+              <div className="pointer-events-none absolute inset-0 flex items-center justify-center bg-[var(--color-surface)] text-[var(--color-text-tertiary)]">
+                <Loader2 size={18} className="animate-spin" aria-label="加载中" />
+              </div>
+            )}
+          </div>
+          <div
+            data-testid="browser-preview-floating-controls"
+            className="pointer-events-none absolute inset-x-0 bottom-0 z-10 flex h-12 items-end justify-end px-3 pb-2"
+          >
+            <div className="pointer-events-auto">
+              {zoomControls}
             </div>
-          )}
+          </div>
         </div>
       </div>
     </div>