refactor(views): split file views into summary, detail, process, and annotations pages

- /files/<id> → new summary page with navigation cards
- /files/<id>/detail → document detail with metadata, preview, text
- /files/<id>/process → processing pipeline status and history
- /files/<id>/annotations → comments & annotations with EmbedPDF viewer
- /files/<id>/comments → redirects to /annotations
- Added embed-pdf-viewer as git submodule for PDF annotation viewer
- Updated all navigation links across templates
- Updated all tests to use new URL structure

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>
Agent-Logs-Url: https://github.com/christianlouis/DocuElevate/sessions/12276514-bd3d-4e3e-84d9-5977d1f82b19

frontend/templates/files.html

@@ -904,7 +904,7 @@
 
     function viewFileDetail(fileId, event) {
       if (event) event.stopPropagation();
-      window.location.href = `/files/${fileId}/detail`;
+      window.location.href = `/files/${fileId}`;
     }
 
     // ── Preview modal ──