fix: resolve file viewer auth issues and add text file viewing support

- Fix file viewer not sending JWT auth tokens when loading files
  - inlineViewer.js: already used XHR with auth (images/PDFs worked)
  - fileViewer.js: was setting img.src/iframe.src directly without auth headers,
    now uses fetch with Bearer token and blob URLs
  - ui.js/contextMenus.js/fileRenderer.js/recent.js/favorites.js: replaced all
    window.location.href = /api/files/... (unauthenticated navigation) with
    authenticated viewer or fileOps.downloadFile()

- Add text file viewing support (text/*, application/json, etc.)
  - New createTextViewer() in inlineViewer.js with authenticated fetch
  - New loadTextViewer() in fileViewer.js with authenticated fetch
  - New isViewableFile() helper in ui.js used across all entry points
  - CSS styles for .inline-viewer-text-content and .file-viewer-text-content

- Translate remaining Spanish strings to English in viewer files

Fixes: text files showing 'Token not provided', images failing to load,
and text files not being previewable at all.

static/css/inlineViewer.css

@@ -193,6 +193,25 @@
   margin: 0 0 16px;
 }
 
+/* Text viewer */
+.inline-viewer-text-content {
+  width: 100%;
+  height: 100%;
+  margin: 0;
+  padding: 16px 24px;
+  font-family: 'Courier New', Consolas, Monaco, monospace;
+  font-size: 14px;
+  line-height: 1.6;
+  color: #2d3748;
+  background-color: #fff;
+  overflow: auto;
+  white-space: pre-wrap;
+  word-wrap: break-word;
+  box-sizing: border-box;
+  text-align: left;
+  tab-size: 4;
+}
+
 /* Responsive adjustments */
 @media (max-width: 768px) {
   .inline-viewer-content {