feat(ai): ajouter une section de la reponse et supporter l'editeur Forge (BUG-057, #102)

L'assistant IA peut desormais inserer sa reponse dans l'editeur Forge (postMessage parent-insert) en plus d'Editer, et chaque bloc de code propose un bouton « Ajouter la section » pour n'inserer que ce bloc.

frontend/style.css

@@ -9531,6 +9531,14 @@ body.popup-mode .content-area {
 .bookslm-bubble.assistant { align-self: flex-start; background: transparent; padding: 0; width: 100%; max-width: 100%; color: var(--text-primary); }
 .bookslm-bubble.assistant code { background: rgba(0,0,0,0.2); padding: 1px 4px; border-radius: 3px; font-size: 0.9em; }
 .bookslm-bubble.assistant pre { background: rgba(0,0,0,0.3); padding: 10px; border-radius: 6px; overflow-x: auto; margin: 8px 0; }
+/* #102 — per-code-block “Ajouter”: a discreet button in the block's corner,
+   revealed on hover/focus, that inserts only this section. */
+.bookslm-code-block { position: relative; }
+.bookslm-code-block .bookslm-code-insert { position: absolute; top: 6px; right: 6px;
+  z-index: 1; background: var(--surface2); border-color: var(--border); opacity: 0;
+  transition: opacity 0.15s; }
+.bookslm-code-block:hover .bookslm-code-insert,
+.bookslm-code-block:focus-within .bookslm-code-insert { opacity: 1; }
 .bookslm-sources { display: flex; flex-wrap: wrap; gap: 4px; margin-top: 8px; }
 .bookslm-source-badge { display: inline-flex; align-items: center; gap: 4px; padding: 2px 8px;
   background: var(--surface); border: 1px solid var(--border); border-radius: 12px;