feat: update all OpenAI/ChatGPT refs + settings dropdown for fixed-value fields

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

frontend/templates/about.html

@@ -18,7 +18,8 @@
       for everyone, whether you're a small startup or a large enterprise.
     </p>
     <p class="text-gray-600">
-      We harness the power of OpenAI for metadata extraction and text refinement, integrate seamlessly
+      We harness the power of pluggable AI providers (OpenAI, Anthropic Claude, Google Gemini, Ollama,
+      OpenRouter, Portkey, and more) for metadata extraction and text refinement, integrate seamlessly
       with Dropbox, Nextcloud, and Paperless NGX for storage and indexing, leverage Azure Document
       Intelligence for OCR, and even use Gotenberg for file-to-PDF conversions.
     </p>
@@ -33,7 +34,7 @@
         <ul class="list-disc list-inside text-gray-600 ml-2">
           <li>Simple and secure file uploads with drag & drop support</li>
           <li>OCR powered by Azure Document Intelligence</li>
-          <li>Automated metadata extraction using OpenAI</li>
+          <li>Automated metadata extraction using a pluggable AI provider</li>
           <li>PDF conversion for various file formats via Gotenberg</li>
           <li>Intelligent document classification and date extraction</li>
         </ul>