feat: add download + copy file content to context menus and editor

- Add /api/pages/{id}/download and /api/pages/{id}/file-content endpoints
- Add Download + Copy content to shared context menu (_ctx_menu.html)
- Wire handlers in local-workspace and library context menus
- Add Download + Copy content to editor '...' menu for file pages
- Multi-block selection copy/cut/paste with Ctrl+C/X/V shortcuts
- Align page title with blocks start (CSS pseudo-element offset)

app/templates/_ctx_menu.html

@@ -12,8 +12,8 @@
   avec la capacité respective de la page au clic.
 
   Handlers attendus (tous optionnels) :
-    open, openTab, peek, folder, rename, setIcon, duplicate, link, move,
-    fav, recent, delete, tagExisting, tagAdd, tagRemove
+    open, openTab, peek, folder, rename, setIcon, duplicate, link, download,
+    copyContent, move, fav, recent, delete, tagExisting, tagAdd, tagRemove
   ############################################################################}
 <script data-cfasync="false">
 /* ═════════════════════════════════════════════════════════════════════
@@ -224,6 +224,18 @@
     <span style="flex:1;">Copy link</span>
   </div>
 
+  {# ── Download file (file pages) ── #}
+  <div class="menu-item" x-show="$store.fdCtx.has('download')" @click="$store.fdCtx.run('download')">
+    <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M21 15v4a2 2 0 01-2 2H5a2 2 0 01-2-2v-4"/><polyline points="7 10 12 15 17 10"/><line x1="12" y1="15" x2="12" y2="3"/></svg>
+    <span style="flex:1;">Download</span>
+  </div>
+
+  {# ── Copy file content (textual file pages) ── #}
+  <div class="menu-item" x-show="$store.fdCtx.has('copyContent')" @click="$store.fdCtx.run('copyContent')">
+    <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><rect x="9" y="9" width="13" height="13" rx="2"/><path d="M5 15H4a2 2 0 01-2-2V4a2 2 0 012-2h9a2 2 0 012 2v1"/></svg>
+    <span style="flex:1;">Copy content</span>
+  </div>
+
   {# ── Move to ── #}
   <div class="menu-item" x-show="$store.fdCtx.has('move')" @click="$store.fdCtx.run('move')">
     <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M22 19a2 2 0 01-2 2H4a2 2 0 01-2-2V5a2 2 0 012-2h5l2 3h9a2 2 0 012 2z"/></svg>