fix: cacher tous les boutons create du sidebar quand aucun workspace actif

- Meetings '+' button → gardé avec has_active_workspace
- Sidebar footer 'New page' → gardé avec has_active_workspace
- Context menu New File/New Folder → déjà gardé car l'arbre est caché sans workspace
- Workspace section déjà gardée (commit précédent)
- 143 tests passent

app/templates/base.html

@@ -262,7 +262,9 @@
           <span>Meetings</span>
         </div>
         <div class="sidebar-section-actions">
+          {% if has_active_workspace %}
           <button class="section-action-btn" title="Add" @click.stop="window.FlowDeck.createPage()">+</button>
+          {% endif %}
         </div>
       </div>
       <div class="sidebar-section-items" x-show="sectionsOpen.meetings" x-transition>
@@ -424,9 +426,11 @@
           <span style="font-size:14px;">💬</span> New chat
           <span class="shortcut">Ctrl+O</span>
         </button>
+        {% if has_active_workspace %}
         <button class="sidebar-footer-btn" style="width:36px; justify-content:center; background:var(--bg-hover); border-radius:8px;" onclick="window.FlowDeck.createPage()" title="New page">
           <svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M14 2H6a2 2 0 00-2 2v16a2 2 0 002 2h12a2 2 0 002-2V8z"/><polyline points="14 2 14 8 20 8"/><line x1="12" y1="18" x2="12" y2="12"/><line x1="9" y1="15" x2="15" y2="15"/></svg>
         </button>
+        {% endif %}
       </div>
     </div>
     </div><!-- /sidebar-scroll -->