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;

static/js/features/files/inlineViewer.js

@@ -251,13 +251,42 @@ class InlineViewer {
   async createBlobUrlViewer(file, type, container, loader) {
     try {
       console.log('Creating blob URL viewer for:', file.name, 'type:', type);
-      
+
+      // Update loader to show progress bar for large files
+      let progressBar = null;
+      let progressText = null;
+      if (loader && file.size > 10 * 1024 * 1024) { // Show progress for files > 10MB
+        loader.innerHTML = `
+          <div class="inline-viewer-progress">
+            <i class="fas fa-spinner fa-spin"></i>
+            <div class="inline-viewer-progress-bar">
+              <div class="inline-viewer-progress-fill" style="width: 0%"></div>
+            </div>
+            <div class="inline-viewer-progress-text">0%</div>
+          </div>
+        `;
+        progressBar = loader.querySelector('.inline-viewer-progress-fill');
+        progressText = loader.querySelector('.inline-viewer-progress-text');
+      }
+
       // Use XMLHttpRequest instead of fetch to get better control over the response
       const xhr = new XMLHttpRequest();
       xhr.open('GET', `/api/files/${file.id}?inline=true`, true);
       xhr.responseType = 'blob';
       xhr.withCredentials = true;
-      
+
+      // Track download progress - use double precision for large file support (>2GB)
+      xhr.onprogress = (e) => {
+        if (e.lengthComputable && progressBar && progressText) {
+          // Use direct division to avoid 32-bit overflow issues
+          // e.loaded and e.total are JavaScript numbers (64-bit float)
+          const progress = e.loaded / e.total;
+          const pct = Math.round(progress * 100);
+          progressBar.style.width = pct + '%';
+          progressText.textContent = pct + '%';
+        }
+      };
+
       // Create a promise to handle the XHR
       const response = await new Promise((resolve, reject) => {
         xhr.onload = function() {
@@ -267,11 +296,11 @@ class InlineViewer {
             reject(new Error(`Error fetching file: ${this.status} ${this.statusText}`));
           }
         };
-        
+
         xhr.onerror = function() {
           reject(new Error('Network error'));
         };
-        
+
         xhr.send();
       });