Add document analysis: page count, text extraction & language detection

Introduces a document analyzer service that extracts page count (via pdf-parse),
text preview, and detected language (via franc) from uploaded files. Analysis runs
automatically on upload (configurable via SystemSettings) and can be triggered
retroactively for existing files. Results are displayed as badges in the FileViewer
and fed to AI screening for language-based filtering criteria.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/admin/round/filtering-dashboard.tsx

@@ -1599,7 +1599,7 @@ function FilteringRulesSection({ roundId }: { roundId: string }) {
                     className="text-sm"
                   />
                   <p className="text-xs text-muted-foreground mt-1">
-                    The AI has access to: category, country, region, founded year, ocean issue, tags, description, file details (type, page count, size), and team size.
+                    The AI has access to: category, country, region, founded year, ocean issue, tags, description, file details (type, page count, size, detected language), and team size.
                   </p>
                 </div>