feat(uat): file preview/download fix, clients-by-country page, residential column picker

Batch #4 UAT items.

1. Documents — clicking any file dumped raw presigned-URL JSON. Was
   systemic: 6 surfaces linked a browser directly at the JSON-returning
   /files/[id]/{download,preview} routes. Those routes now 302-redirect
   when called with ?redirect=1 (default stays JSON for the dialog +
   interest-eoi-tab programmatic consumers); the six <Link> sites use it.
   The documents-hub file row now opens the inline FilePreviewDialog +
   has a per-row Download button, and the preview dialog header gained a
   persistent Download button for all file types.

2. Clients-by-country — the widget's "+N more" dead text is now a
   "Show all" link to a new /clients/by-country page rendering the full
   ranked country breakdown (each row drills into the filtered list).

3. Residential clients list — moved off its bespoke table onto the
   shared DataTable + ColumnPicker (same UX as clients/interests). Adds
   a "Date added" column, default-hides the empty "Residence" column,
   preserves the mobile card view, persists per-user column choices.

tsc clean, eslint clean, 1584/1584 vitest.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/components/files/file-preview-dialog.tsx

@@ -121,12 +121,24 @@ export function FilePreviewDialog({
         <DialogHeader>
           <DialogTitle className="flex items-center gap-2 truncate">
             <span className="truncate">{fileName ?? 'Preview'}</span>
+            {fileId && (
+              <a
+                href={`/api/v1/files/${fileId}/download?redirect=1`}
+                className="shrink-0 text-muted-foreground hover:text-foreground"
+                title="Download"
+                aria-label={`Download ${fileName ?? 'file'}`}
+              >
+                <Download className="h-4 w-4" />
+              </a>
+            )}
             {previewUrl && (
               <a
                 href={previewUrl}
                 target="_blank"
                 rel="noopener noreferrer"
                 className="shrink-0 text-muted-foreground hover:text-foreground"
+                title="Open in new tab"
+                aria-label="Open in new tab"
               >
                 <ExternalLink className="h-4 w-4" />
               </a>