i18n: translate 6 HTML Jinja2 templates with _() calls

Replace all hardcoded English visible text with {{ _("key") }} calls in:
- queue_dashboard.html: headings, stat cards, table headers, empty states
- api_tokens.html: form labels, table headers, status badges, aria-labels
- similarity_dashboard.html: headings, stat labels, controls, empty states
- backup.html: buttons, config labels, table, retention section, confirm dialog
- shared_links.html: form labels/options, table headers, status badges
- duplicates.html: tabs, role tags, near-dup form, explanation bullets

Follows i18n rules: placeholder/aria-label/title attrs translated,
JS strings in <script> left as-is, Alpine.js bindings use Jinja2
server-side evaluation pattern for dynamic translated strings.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

frontend/templates/upload.html

@@ -1,28 +1,28 @@
 {% extends "base.html" %}
-{% block title %}Upload Document{% endblock %}
+{% block title %}{{ _("upload.page_title") }}{% endblock %}
 
 {% block content %}
 <div class="flex flex-col items-center justify-center p-4 sm:p-8">
-  <h1 class="text-2xl sm:text-3xl font-bold mb-6 sm:mb-8">Upload Files</h1>
+  <h1 class="text-2xl sm:text-3xl font-bold mb-6 sm:mb-8">{{ _("upload.page_title") }}</h1>
 
   <!-- File Upload Section -->
   <div class="w-full max-w-2xl mb-6 sm:mb-8">
-    <h2 class="text-xl font-semibold mb-4">Upload from Device</h2>
+    <h2 class="text-xl font-semibold mb-4">{{ _("upload.section_device") }}</h2>
     <form action="/api/ui-upload" method="POST" enctype="multipart/form-data">
       <div
         id="dropZone"
         class="border-4 border-dashed border-gray-300 rounded-lg p-6 sm:p-8 bg-white text-center w-full"
         role="button"
         tabindex="0"
-        aria-label="File upload area. Drag and drop files here, or press Enter to browse files."
+        aria-label="{{ _('upload.drop_zone_aria') }}"
         ondragover="handleDragOver(event)"
         ondragleave="handleDragLeave(event)"
       >
         <p class="text-gray-500 mb-4 hidden sm:block">
-          Drag &amp; drop files or folders here, or click to select files.
+          {{ _("upload.drop_hint_desktop") }}
         </p>
         <p class="text-gray-500 mb-4 sm:hidden">
-          Tap to select files or use the camera button below.
+          {{ _("upload.drop_hint_mobile") }}
         </p>
         <input
           id="fileInput"
@@ -31,7 +31,7 @@
           onchange="handleFileSelect(event)"
           name="files"
           multiple
-          aria-label="Select files to upload"
+          aria-label="{{ _('upload.select_file') }}"
           accept="application/pdf,application/msword,application/vnd.openxmlformats-officedocument.wordprocessingml.document,application/vnd.ms-excel,application/vnd.openxmlformats-officedocument.spreadsheetml.sheet,application/vnd.ms-powerpoint,application/vnd.openxmlformats-officedocument.presentationml.presentation,image/*"
         />
         <!-- Browse Files button (all devices) -->
@@ -41,11 +41,11 @@
           class="bg-blue-500 hover:bg-blue-700 text-white font-bold py-3 px-6 rounded-lg transition duration-200 mb-4"
           style="min-height:44px;"
         >
-          <i class="fas fa-folder-open mr-2" aria-hidden="true"></i> Browse Files
+          <i class="fas fa-folder-open mr-2" aria-hidden="true"></i> {{ _("upload.browse_button") }}
         </button>
         <div class="text-sm text-gray-500 mt-2">
-          <p>Allowed types: PDF, Office documents (Word, Excel, PowerPoint, etc.), Images</p>
-          <p>Maximum size: 500MB per file &bull; Directories are uploaded recursively</p>
+          <p>{{ _("upload.file_types") }}</p>
+          <p>{{ _("upload.file_size_hint") }}</p>
         </div>
       </div>
 
@@ -55,7 +55,7 @@
           class="w-full flex items-center justify-center gap-2 bg-green-500 hover:bg-green-700 text-white font-bold py-3 px-6 rounded-lg transition duration-200 cursor-pointer"
           style="min-height:44px;"
         >
-          <i class="fas fa-camera" aria-hidden="true"></i> Take Photo / Scan Document
+          <i class="fas fa-camera" aria-hidden="true"></i> {{ _("upload.camera_button") }}
           <input
             id="cameraInput"
             type="file"
@@ -63,7 +63,7 @@
             onchange="handleFileSelect(event)"
             accept="image/*"
             capture="environment"
-            aria-label="Take photo or scan document"
+            aria-label="{{ _('upload.camera_button') }}"
           />
         </label>
       </div>
@@ -72,40 +72,40 @@
 
   <!-- URL Upload Section -->
   <div class="w-full max-w-2xl mb-6 sm:mb-8">
-    <h2 class="text-xl font-semibold mb-4">Upload from URL</h2>
+    <h2 class="text-xl font-semibold mb-4">{{ _("upload.section_url") }}</h2>
     <div class="bg-white border border-gray-300 rounded-lg p-4 sm:p-6">
       <form id="urlUploadForm" class="space-y-4">
         <div>
           <label for="urlInput" class="block text-sm font-medium text-gray-700 mb-2">
-            File URL
+            {{ _("upload.url_label") }}
           </label>
           <input
             type="url"
             id="urlInput"
             name="url"
-            placeholder="https://example.com/document.pdf"
+            placeholder="{{ _('upload.url_placeholder') }}"
             class="w-full px-4 py-3 border border-gray-300 rounded-lg focus:outline-none focus:ring-2 focus:ring-blue-500"
             style="min-height:44px;"
             required
           />
           <p class="text-sm text-gray-500 mt-1">
-            Enter a direct link to a file (PDF, Office documents, or images)
+            {{ _("upload.url_description") }}
           </p>
         </div>
         <div>
           <label for="urlFilename" class="block text-sm font-medium text-gray-700 mb-2">
-            Filename (optional)
+            {{ _("upload.filename_label") }}
           </label>
           <input
             type="text"
             id="urlFilename"
             name="filename"
-            placeholder="my-document.pdf"
+            placeholder="{{ _('upload.filename_placeholder') }}"
             class="w-full px-4 py-3 border border-gray-300 rounded-lg focus:outline-none focus:ring-2 focus:ring-blue-500"
             style="min-height:44px;"
           />
           <p class="text-sm text-gray-500 mt-1">
-            Leave empty to use filename from URL
+            {{ _("upload.filename_description") }}
           </p>
         </div>
         <button
@@ -113,7 +113,7 @@
           class="w-full bg-blue-500 hover:bg-blue-700 text-white font-bold py-3 px-4 rounded-lg transition duration-200"
           style="min-height:44px;"
         >
-          Download and Process
+          {{ _("upload.download_button") }}
         </button>
       </form>
       <div id="urlStatusMessage" class="mt-4" aria-live="polite"></div>