feat: add backslash shortcut to toggle editor panel

Added \ key to toggle the editor panel open/closed:
- Opens to 'document' tab when panel is closed
- Closes panel when it's open
- Updated button tooltips to indicate the keyboard shortcut

Works in all contexts (main document and iframe).

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

src/components/editor/EditorPanel.vue

@@ -6,6 +6,7 @@
         class="tab"
         :class="{ active: activeTab === 'document' }"
         @click="activeTab = 'document'"
+        title="Ouvrir l'onglet Document (\)"
       >
         Document
       </button>
@@ -14,6 +15,7 @@
         class="tab"
         :class="{ active: activeTab === 'code' }"
         @click="activeTab = 'code'"
+        title="Ouvrir l'onglet Code"
       >
         Code
       </button>
@@ -22,6 +24,7 @@
         class="tab"
         :class="{ active: activeTab === 'contenu' }"
         @click="activeTab = 'contenu'"
+        title="Ouvrir l'onglet Contenu"
       >
         Contenu
       </button>
@@ -32,7 +35,7 @@
       type="button"
       class="close-button"
       @click="activeTab = ''"
-      title="Fermer le panneau"
+      title="Fermer le panneau (\)"
     >
       <svg
         xmlns="http://www.w3.org/2000/svg"