Manual save button, file requirement labels, fix config revert bug

- Replace auto-save with manual floating save bar that appears when config
  has unsaved changes (Discard / Save Changes buttons). Fixes race condition
  where server sync overwrote local state after toggling switches.
- Show file requirement name (e.g. "Pitch Deck", "Presentation") above each
  document in the All Uploaded Files section on project detail page
- Pass requirement relation data through to FileViewer component

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

src/components/shared/file-viewer.tsx

@@ -258,6 +258,11 @@ function FileItem({ file }: { file: ProjectFile }) {
         </div>
 
         <div className="flex-1 min-w-0">
+          {file.requirement && (
+            <p className="text-xs font-semibold text-primary/80 mb-0.5 uppercase tracking-wide">
+              {file.requirement.name}
+            </p>
+          )}
           <div className="flex items-center gap-2">
             <p className="font-medium truncate">{file.fileName}</p>
             {file.version != null && file.version > 1 && (