fix(inline-viewer): add download progress bar for files >2GB

Add download progress tracking to createBlobUrlViewer to fix incorrect
progress display for large files. Changes:

- Add xhr.onprogress handler to track download bytes
- Use 64-bit float division to avoid 32-bit integer overflow
- Show progress bar UI for files >10MB with percentage
- Add CSS styles with dark theme support

The progress calculation now correctly handles files larger than 2GB
by using JavaScript's native double-precision floats instead of
operations that might truncate to 32-bit integers.

Fixes #82

static/css/views/inlineViewer.css

@@ -171,6 +171,56 @@
   color: #64748b;
 }
 
+/* Download progress container */
+.inline-viewer-progress {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 12px;
+  padding: 20px;
+  background: rgba(255, 255, 255, 0.95);
+  border-radius: 8px;
+  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
+}
+
+/* Progress bar track */
+.inline-viewer-progress-bar {
+  width: 200px;
+  height: 8px;
+  background: #e2e8f0;
+  border-radius: 4px;
+  overflow: hidden;
+}
+
+/* Progress bar fill */
+.inline-viewer-progress-fill {
+  height: 100%;
+  background: linear-gradient(90deg, #3b82f6, #60a5fa);
+  border-radius: 4px;
+  transition: width 0.2s ease;
+}
+
+/* Progress percentage text */
+.inline-viewer-progress-text {
+  font-size: 14px;
+  font-weight: 600;
+  color: #475569;
+  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
+}
+
+/* Dark theme support */
+[data-theme="dark"] .inline-viewer-progress {
+  background: rgba(30, 41, 59, 0.95);
+}
+
+[data-theme="dark"] .inline-viewer-progress-bar {
+  background: #334155;
+}
+
+[data-theme="dark"] .inline-viewer-progress-text {
+  color: #cbd5e1;
+}
+
 /* Error and unsupported message */
 .inline-viewer-message {
   padding: 32px;