refactor(ui): improve slash menu layout and add shortcut hints

- increase menu width and max height constants
- add SHORTCUT_HINT map displaying markdown shortcuts per block type
- update empty state and list container to use rounded-lg and shadow-md
- add section label header above block items
- show monospace shortcut hint on each menu item
- tighten item padding and icon size for denser layout

src/shared/components/BlockEditor/SlashMenu.client.js

@@ -2,9 +2,24 @@
 
 import React, { useEffect, useLayoutEffect, useMemo, useRef, useState } from 'react';
 
-const MENU_WIDTH = 256;       // w-64
-const MENU_MAX_HEIGHT = 288;  // max-h-72
+const MENU_WIDTH = 280;
+const MENU_MAX_HEIGHT = 320;
 const VIEWPORT_MARGIN = 8;
+
+const SHORTCUT_HINT = {
+  paragraph: '',
+  heading_1: '#',
+  heading_2: '##',
+  heading_3: '###',
+  heading_4: '####',
+  heading_5: '#####',
+  heading_6: '######',
+  bullet_item: '-',
+  numbered_item: '1.',
+  quote: '>',
+  code: '```',
+  divider: '---',
+};
 import { listBlocks } from './blockRegistry.js';
 
 // Menu flottant des commandes. Affiché ancré à un élément (anchorRect).
@@ -92,8 +107,8 @@ export default function SlashMenu({
   if (items.length === 0) {
     return (
       <div
-        className="fixed z-50 w-64 rounded-xl border border-neutral-200 dark:border-neutral-700 bg-white dark:bg-neutral-900 shadow-lg p-3 text-sm text-neutral-500"
-        style={{ top, left, maxHeight }}
+        className="fixed z-50 rounded-lg border border-neutral-200 dark:border-neutral-700 bg-white dark:bg-neutral-900 shadow-md px-3 py-2 text-xs text-neutral-500"
+        style={{ top, left, width: MENU_WIDTH, maxHeight }}
       >
         Aucune commande pour « {query} »
       </div>
@@ -103,12 +118,16 @@ export default function SlashMenu({
   return (
     <div
       ref={listRef}
-      className="fixed z-50 w-64 overflow-y-auto rounded-xl border border-neutral-200 dark:border-neutral-700 bg-white dark:bg-neutral-900 shadow-lg py-1"
-      style={{ top, left, maxHeight }}
+      className="fixed z-50 overflow-y-auto rounded-lg border border-neutral-200 dark:border-neutral-700 bg-white dark:bg-neutral-900 shadow-md py-1"
+      style={{ top, left, width: MENU_WIDTH, maxHeight }}
       onMouseDown={(e) => e.preventDefault()} // ne pas voler le focus
     >
+      <div className="px-3 pt-1.5 pb-1 text-[10px] font-medium uppercase tracking-wider text-neutral-400 dark:text-neutral-500">
+        Blocs de base
+      </div>
       {items.map((def, i) => {
         const active = i === selectedIndex;
+        const hint = SHORTCUT_HINT[def.type];
         return (
           <button
             key={def.type}
@@ -116,14 +135,19 @@ export default function SlashMenu({
             data-slash-index={i}
             onMouseEnter={() => onHoverIndex?.(i)}
             onClick={() => onSelect?.(def.type)}
-            className={`w-full flex items-center gap-3 px-3 py-2 text-left text-sm transition-colors ${active ? 'bg-neutral-100 dark:bg-neutral-800' : 'hover:bg-neutral-50 dark:hover:bg-neutral-800/60'}`}
+            className={`w-full flex items-center gap-2.5 px-2 py-1 text-left transition-colors ${active ? 'bg-neutral-100 dark:bg-neutral-800' : ''}`}
           >
-            <span className="w-7 h-7 flex items-center justify-center rounded-md border border-neutral-200 dark:border-neutral-700 text-xs font-medium text-neutral-700 dark:text-neutral-300">
+            <span className="w-6 h-6 flex items-center justify-center rounded-[5px] border border-neutral-200 dark:border-neutral-700 text-[11px] font-medium text-neutral-700 dark:text-neutral-300 flex-shrink-0">
               {def.icon}
             </span>
-            <span className="flex-1 min-w-0 truncate text-neutral-900 dark:text-white">
+            <span className="flex-1 min-w-0 truncate text-[13px] text-neutral-900 dark:text-white">
               {def.label}
             </span>
+            {hint && (
+              <span className="text-[11px] font-mono text-neutral-400 dark:text-neutral-500 flex-shrink-0">
+                {hint}
+              </span>
+            )}
           </button>
         );
       })}