refactor(web-test): replace fade transitions with auto-cleanup of overlays

CSS fade transitions don't work well with CDP screencast (causes desktop
flash between slides). Instead, showImage/showTitleSlide now automatically
remove the other overlay type — no need to call hide before showing next.

Pattern for consecutive slides:
  showTitleSlide(...) → showImage(...) → showImage(...) → hideImage()
No hideTitleSlide() needed between title and first image.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.claude/skills/web-test/scripts/browser.mjs

@@ -4213,8 +4213,7 @@ export async function showTitleSlide(text, opts = {}) {
 
   await page.evaluate(({ text, subtitle, background, color, fontSize }) => {
     let div = document.getElementById('__web_test_title');
-    const isNew = !div;
+    if (!div) {
-    if (isNew) {
       div = document.createElement('div');
       div.id = '__web_test_title';
       document.body.appendChild(div);
@@ -4224,15 +4223,16 @@ export async function showTitleSlide(text, opts = {}) {
       `background:${background}`,
       'display:flex', 'align-items:center', 'justify-content:center',
       'z-index:999999', 'pointer-events:none',
-      'transition:opacity 0.3s ease', isNew ? 'opacity:0' : ''
     ].join(';');
+    // Remove other overlays to prevent flash between slides
+    const img = document.getElementById('__web_test_image');
+    if (img) img.remove();
     const esc = s => s.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/\n/g, '<br>');
     let html = `<div style="font-size:${fontSize}px;font-weight:600;line-height:1.4;">${esc(text)}</div>`;
     if (subtitle) {
       html += `<div style="font-size:${Math.round(fontSize * 0.5)}px;margin-top:16px;opacity:0.7;">${esc(subtitle)}</div>`;
     }
     div.innerHTML = `<div style="text-align:center;max-width:70%;color:${color};font-family:'Segoe UI',Arial,sans-serif;">${html}</div>`;
-    if (isNew) requestAnimationFrame(() => { div.style.opacity = '1'; });
   }, { text, subtitle, background, color, fontSize });
 
   // Smart TTS wait (same pattern as showCaption/showImage)
@@ -4248,22 +4248,13 @@ export async function showTitleSlide(text, opts = {}) {
   }
 }
 
-/** Remove the title slide overlay (with fade-out). */
+/** Remove the title slide overlay. */
 export async function hideTitleSlide() {
   ensureConnected();
-  const exists = await page.evaluate(() => {
+  await page.evaluate(() => {
     const el = document.getElementById('__web_test_title');
-    if (!el) return false;
+    if (el) el.remove();
-    el.style.opacity = '0';
-    return true;
   });
-  if (exists) {
-    await page.waitForTimeout(350);
-    await page.evaluate(() => {
-      const el = document.getElementById('__web_test_title');
-      if (el) el.remove();
-    });
-  }
 }
 
 /**
@@ -4337,18 +4328,20 @@ export async function showImage(imagePath, opts = {}) {
 
   await page.evaluate(({ dataUrl, fit, bg, useBlur, shadow, maxSize, isFull }) => {
     let div = document.getElementById('__web_test_image');
-    const isNew = !div;
+    if (!div) {
-    if (isNew) {
       div = document.createElement('div');
       div.id = '__web_test_image';
       document.body.appendChild(div);
     }
+    // Remove other overlays to prevent flash between slides
+    const title = document.getElementById('__web_test_title');
+    if (title) title.remove();
+
     div.style.cssText = [
       'position:fixed', 'top:0', 'left:0', 'width:100%', 'height:100%',
       `background:${bg}`,
       'display:flex', 'align-items:center', 'justify-content:center',
-      'z-index:999999', 'pointer-events:none', 'overflow:hidden',
+      'z-index:999999', 'pointer-events:none', 'overflow:hidden'
-      'transition:opacity 0.3s ease', isNew ? 'opacity:0' : ''
     ].join(';');
 
     let html = '';
@@ -4366,7 +4359,6 @@ export async function showImage(imagePath, opts = {}) {
     html += `<img src="${dataUrl}" style="position:relative;${sizeCss}${shadowCss}" />`;
 
     div.innerHTML = html;
-    if (isNew) requestAnimationFrame(() => { div.style.opacity = '1'; });
   }, { dataUrl, fit, bg, useBlur, shadow, maxSize, isFull });
 
   // Smart TTS wait (same pattern as showCaption)
@@ -4382,22 +4374,13 @@ export async function showImage(imagePath, opts = {}) {
   }
 }
 
-/** Remove the image overlay (with fade-out). */
+/** Remove the image overlay. */
 export async function hideImage() {
   ensureConnected();
-  const exists = await page.evaluate(() => {
+  await page.evaluate(() => {
     const el = document.getElementById('__web_test_image');
-    if (!el) return false;
+    if (el) el.remove();
-    el.style.opacity = '0';
-    return true;
   });
-  if (exists) {
-    await page.waitForTimeout(350);
-    await page.evaluate(() => {
-      const el = document.getElementById('__web_test_image');
-      if (el) el.remove();
-    });
-  }
 }
 
 /**