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/js/ui.js

@@ -434,6 +434,24 @@ const ui = {
         }
     },
 
+    /**
+     * Check if a file can be previewed in the viewer
+     * @param {Object} file - File object with mime_type property
+     * @returns {boolean}
+     */
+    isViewableFile(file) {
+        if (!file || !file.mime_type) return false;
+        if (file.mime_type.startsWith('image/')) return true;
+        if (file.mime_type === 'application/pdf') return true;
+        if (file.mime_type.startsWith('text/')) return true;
+        const textTypes = [
+            'application/json', 'application/xml', 'application/javascript',
+            'application/x-sh', 'application/x-yaml', 'application/toml',
+            'application/x-toml', 'application/sql',
+        ];
+        return textTypes.includes(file.mime_type);
+    },
+
     /**
      * Show notification
      * @param {string} title - Notification title
@@ -957,17 +975,16 @@ const ui = {
             }
             
             // Check if it's a viewable file type
-            if ((file.mime_type && file.mime_type.startsWith('image/')) || 
-                (file.mime_type && file.mime_type === 'application/pdf')) {
+            if (this.isViewableFile(file)) {
                 if (window.inlineViewer) {
                     window.inlineViewer.openFile(file);
                 } else if (window.fileViewer) {
                     window.fileViewer.open(file);
                 } else {
-                    window.location.href = `/api/files/${file.id}`;
+                    window.fileOps.downloadFile(file.id, file.name);
                 }
             } else {
-                window.location.href = `/api/files/${file.id}`;
+                window.fileOps.downloadFile(file.id, file.name);
             }
         });
 
@@ -1051,8 +1068,7 @@ const ui = {
             }
             
             // Check if it's a viewable file type
-            if ((file.mime_type && file.mime_type.startsWith('image/')) || 
-                (file.mime_type && file.mime_type === 'application/pdf')) {
+            if (this.isViewableFile(file)) {
                 // Open in the inline viewer
                 if (window.inlineViewer) {
                     window.inlineViewer.openFile(file);
@@ -1061,11 +1077,11 @@ const ui = {
                     window.fileViewer.open(file);
                 } else {
                     // No viewer available, download directly
-                    window.location.href = `/api/files/${file.id}`;
+                    window.fileOps.downloadFile(file.id, file.name);
                 }
             } else {
                 // For other file types, download directly
-                window.location.href = `/api/files/${file.id}`;
+                window.fileOps.downloadFile(file.id, file.name);
             }
         });