feat(uat-batch-4): a11y form primitives + click-to-preview + EOI empty-state + lint guards

- FieldError primitive (role=alert, aria-live) — used by Wave 3
  form-error UX work.
- FieldLabel primitive (Label + Info-tooltip slot) — foundational for
  the platform-wide admin-settings tooltip audit.
- ESLint guard against em-dash in user-facing JSX text inside
  src/components + src/app (warning, not error; 111 existing instances
  flagged for follow-up sweep).
- FileGrid card body becomes click-to-preview button (was hidden under
  a kebab); aria-label per row; kebab keeps Download/Rename/Delete.
- DocumentList: title cell on rows with signedFileId opens
  FilePreviewDialog; kebab gains Download action (was missing
  per UAT). Single FilePreviewDialog instance lifted to the parent.
- DocumentList type extended with signedFileId.
- EOI empty state: third ghost button "Mark signed without file"
  wired to existing MarkExternallySignedDialog (parity with
  reservation tab).
- Watcher empty-state padding fix on document-detail.

tsc clean. 1419/1419 vitest. lint clean on touched files.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/files/file-grid.tsx

@@ -2,7 +2,6 @@
 
 import {
   Download,
-  Eye,
   FileText,
   Film,
   Image,
@@ -22,7 +21,6 @@ import {
   DropdownMenuTrigger,
 } from '@/components/ui/dropdown-menu';
 import { Skeleton } from '@/components/ui/skeleton';
-import { PREVIEWABLE_MIMES } from '@/lib/constants/file-validation';
 
 export interface FileRow {
   id: string;
@@ -102,9 +100,14 @@ export function FileGrid({
       {files.map((file) => (
         <div
           key={file.id}
-          className="group relative rounded-lg border bg-card p-3 hover:border-primary/50 hover:shadow-sm transition-all"
+          className="group relative rounded-lg border bg-card hover:border-primary/50 hover:shadow-sm transition-all"
         >
-          <div className="flex flex-col items-center gap-2">
+          <button
+            type="button"
+            onClick={() => onPreview(file)}
+            aria-label={`Preview ${file.filename}`}
+            className="flex w-full flex-col items-center gap-2 rounded-lg p-3 text-left focus:outline-none focus:ring-2 focus:ring-ring"
+          >
             <FileIcon mimeType={file.mimeType} />
             <p className="w-full truncate text-center text-xs font-medium" title={file.filename}>
               {file.filename}
@@ -113,7 +116,7 @@ export function FileGrid({
               <span>{formatBytes(file.sizeBytes)}</span>
               <span>{format(new Date(file.createdAt), 'MMM d, yyyy')}</span>
             </div>
-          </div>
+          </button>
 
           <div className="absolute right-1 top-1 opacity-0 group-hover:opacity-100 transition-opacity">
             <DropdownMenu>
@@ -127,12 +130,6 @@ export function FileGrid({
                   <Download className="mr-2 h-3.5 w-3.5" />
                   Download
                 </DropdownMenuItem>
-                {file.mimeType && PREVIEWABLE_MIMES.has(file.mimeType) && (
-                  <DropdownMenuItem onClick={() => onPreview(file)}>
-                    <Eye className="mr-2 h-3.5 w-3.5" />
-                    Preview
-                  </DropdownMenuItem>
-                )}
                 <DropdownMenuItem onClick={() => onRename(file)}>
                   <Pencil className="mr-2 h-3.5 w-3.5" />
                   Rename