feat: add document edit functionality with multi-vehicle support (refs #31)

Implemented comprehensive document editing capabilities:

1. Created EditDocumentDialog component:
   - Responsive MUI Dialog with fullScreen on mobile
   - Wraps DocumentForm in edit mode
   - Proper close handlers with refetch

2. Enhanced DocumentForm to support edit mode:
   - Added mode prop ('create' | 'edit')
   - Pre-populate all fields from initialValues
   - Use useUpdateDocument hook when in edit mode
   - Multi-select for shared vehicles (insurance only)
   - Vehicle and document type disabled in edit mode
   - Optional file upload in edit mode
   - Dynamic button text (Create/Save Changes)

3. Updated DocumentDetailPage:
   - Added Edit button with proper touch targets
   - Integrated EditDocumentDialog
   - Refetch document on successful edit

Mobile-first implementation:
- All touch targets >= 44px
- Dialog goes fullScreen on mobile
- Form fields stack on mobile
- Shared vehicle checkboxes have min-h-[44px]
- Buttons use flex-wrap for mobile overflow

Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/features/documents/components/EditDocumentDialog.tsx

@@ -0,0 +1,75 @@
+import React from 'react';
+import {
+  Dialog,
+  DialogTitle,
+  DialogContent,
+  IconButton,
+  useMediaQuery,
+  useTheme,
+} from '@mui/material';
+import CloseIcon from '@mui/icons-material/Close';
+import { DocumentForm } from './DocumentForm';
+import type { DocumentRecord } from '../types/documents.types';
+
+interface EditDocumentDialogProps {
+  open: boolean;
+  onClose: () => void;
+  document: DocumentRecord;
+}
+
+export const EditDocumentDialog: React.FC<EditDocumentDialogProps> = ({
+  open,
+  onClose,
+  document,
+}) => {
+  const theme = useTheme();
+  const isSmall = useMediaQuery(theme.breakpoints.down('sm'));
+
+  return (
+    <Dialog
+      open={open}
+      onClose={onClose}
+      fullScreen={isSmall}
+      maxWidth="md"
+      fullWidth
+      PaperProps={{
+        sx: {
+          maxHeight: isSmall ? '100%' : '90vh',
+          m: isSmall ? 0 : 2,
+        },
+      }}
+    >
+      {isSmall && (
+        <IconButton
+          aria-label="close"
+          onClick={onClose}
+          sx={{
+            position: 'absolute',
+            right: 8,
+            top: 8,
+            color: (theme) => theme.palette.grey[500],
+            zIndex: 1,
+          }}
+        >
+          <CloseIcon />
+        </IconButton>
+      )}
+
+      <DialogTitle sx={{ pb: 1 }}>Edit Document</DialogTitle>
+
+      <DialogContent sx={{ pt: 2 }}>
+        <DocumentForm
+          mode="edit"
+          documentId={document.id}
+          initialValues={document}
+          onSuccess={() => {
+            onClose();
+          }}
+          onCancel={onClose}
+        />
+      </DialogContent>
+    </Dialog>
+  );
+};
+
+export default EditDocumentDialog;