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/_page_editor_content.html

@@ -457,6 +457,15 @@
                     <div class="more-menu-item" @click="exportPage('site')"> Site statique (.zip)</div>
                   </div>
                 </template>
+                <template x-if="contentFormat === 'file' && fileUrl">
+                  <div class="more-menu-sep"></div>
+                  <div class="more-menu-item" @click="downloadFile()">
+                    {{ fd_icon("download",14) }} Download
+                  </div>
+                  <div class="more-menu-item" @click="copyFileContent()">
+                    {{ fd_icon("copy",14) }} Copy content
+                  </div>
+                </template>
                 <div class="more-menu-item" @click="duplicatePage">
                     {{ fd_icon("copy",14) }} Duplicate
                 </div>