Auto-generate on upload, fill preview, fix re-upload

- Auto-generate: selecting a file immediately renders it (no separate
  Generate click needed)
- Auto-fit zoom now scales UP to fill the preview area, not just down
  to fit width. Uses min(scaleW, scaleH) to fit the limiting dimension.
- Fix re-upload: reset fileInput.value on click so selecting the same
  file again triggers the change event
- Patterns also auto-fit to fill the preview

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

static/app.js

@@ -80,6 +80,9 @@ fileInput.addEventListener('change', () => {
   if (fileInput.files.length) setFile(fileInput.files[0]);
 });
 
+// Reset file input after each use so re-selecting the same file triggers change
+fileInput.addEventListener('click', () => { fileInput.value = ''; });
+
 clearFile.addEventListener('click', e => {
   e.stopPropagation();
   currentFile = null;
@@ -105,6 +108,11 @@ function setFile(file) {
   dropZone.style.display = 'none';
   fileInfo.style.display = 'flex';
   generateBtn.disabled = false;
+
+  // Auto-generate immediately on file select
+  if (currentMode === 'image') {
+    generateImage();
+  }
 }
 
 // ── Sliders ──────────────────────────────
@@ -317,14 +325,21 @@ function setZoom(scale) {
 
 function autoFitZoom() {
   requestAnimationFrame(() => {
-    const containerWidth = previewArea.clientWidth - 24;
+    // Reset to base size to measure natural dimensions
     previewArea.style.fontSize = '5px';
     zoomScale = 1.0;
-    const artWidth = previewArea.scrollWidth;
-    if (artWidth > containerWidth && artWidth > 0) {
-      setZoom(containerWidth / artWidth);
-    } else {
-      zoomLevel.textContent = '100%';
+
+    const containerW = previewArea.clientWidth - 16;
+    const containerH = previewArea.clientHeight - 16;
+    const artW = previewArea.scrollWidth;
+    const artH = previewArea.scrollHeight;
+
+    if (artW > 0 && artH > 0) {
+      // Scale to fill the preview area (fit the limiting dimension)
+      const scaleW = containerW / artW;
+      const scaleH = containerH / artH;
+      const fitScale = Math.min(scaleW, scaleH);
+      setZoom(Math.max(0.1, fitScale));
     }
   });
 }