Add screenshot + fullscreen buttons, based on quality audit

New toolbar buttons on every animation:
- 📷 Screenshot: one-click PNG export via canvas.toDataURL()
- ⛶ Fullscreen: toggle browser fullscreen mode

These were identified as top missing features in the learning
system analysis (quality audit of 113 animations).

Also saved audit findings to memory for future sessions:
- 25 animations missing mouse interaction (backfill needed)
- Gallery filter system has tag mismatches
- Oversaturated: attractors (16), underrepresented: sacred geometry,
  chemistry, sound visualization

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

Author: danlex

shared-ui.js

@@ -723,6 +723,21 @@
     uploadBtn.title = 'Upload MP3';
     toolbar.appendChild(uploadBtn);
 
+    // Screenshot button
+    const screenshotBtn = document.createElement('button');
+    screenshotBtn.className = 'tool-btn';
+    screenshotBtn.innerHTML = '📷'; // camera
+    screenshotBtn.title = 'Save Screenshot';
+    toolbar.appendChild(screenshotBtn);
+
+    // Fullscreen button
+    const fsBtn = document.createElement('button');
+    fsBtn.className = 'tool-btn';
+    fsBtn.innerHTML = '⛶'; // expand
+    fsBtn.title = 'Fullscreen';
+    fsBtn.style.fontSize = '14px';
+    toolbar.appendChild(fsBtn);
+
     // Hidden file input
     const audioFileInput = document.createElement('input');
     audioFileInput.type = 'file';
@@ -828,6 +843,31 @@
       copyToClipboard(code, embedBtn);
     });
 
+    // Screenshot button
+    screenshotBtn.addEventListener('click', () => {
+      const canvas = document.querySelector('canvas');
+      if (!canvas) return;
+      const link = document.createElement('a');
+      link.download = `${pageName.toLowerCase().replace(/\s+/g, '-')}.png`;
+      link.href = canvas.toDataURL('image/png');
+      link.click();
+      showToast('Screenshot saved');
+    });
+
+    // Fullscreen button
+    fsBtn.addEventListener('click', () => {
+      if (document.fullscreenElement) {
+        document.exitFullscreen();
+        fsBtn.innerHTML = '⛶';
+      } else {
+        document.documentElement.requestFullscreen();
+        fsBtn.innerHTML = '✕'; // X to exit
+      }
+    });
+    document.addEventListener('fullscreenchange', () => {
+      if (!document.fullscreenElement) fsBtn.innerHTML = '⛶';
+    });
+
     // ESC to close panels + stop audio
     document.addEventListener('keydown', (e) => {
       if (e.key === 'Escape') {