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)

static/css/app.css

@@ -2213,6 +2213,7 @@ button.breadcrumb-current { max-width: 260px; }
   display: flex;
   align-items: flex-start;
   gap: 8px;
+  position: relative;
 }
 
 .page-icon-emoji {
@@ -2296,6 +2297,24 @@ button.breadcrumb-current { max-width: 260px; }
   border-radius: 3px;
   fill: var(--text-dim);
 }
+
+/* Align page title content with blocks (accounting for drag handle offset) */
+.page-title-block::before {
+  content: '';
+  position: absolute;
+  left: -40px;
+  width: 24px;
+  height: 24px;
+}
+
+.page-title-block .page-icon-emoji {
+  margin-left: 8px;
+}
+
+.page-title-block .page-title-input {
+  padding-left: 4px;
+}
+
 .block-handle.visible {
   opacity: 1;
 }
@@ -3550,6 +3569,7 @@ button.breadcrumb-current { max-width: 260px; }
   .page-cover-area { padding: 32px 32px 8px; }
   .blocks-container { padding: 8px 32px 80px; }
   .block-handle { left: -32px; }
+  .page-title-block::before { left: -32px; }
   .page-title-input { font-size: 32px; }
 
   .kanban-column { min-width: 240px; max-width: 300px; }
@@ -3629,6 +3649,9 @@ button.breadcrumb-current { max-width: 260px; }
   .blocks-container { padding: 8px 16px 96px; }
   .block-handle { display: none; }
   .block-actions { display: none; }
+  .page-title-block::before { display: none; }
+  .page-title-block .page-icon-emoji { margin-left: 0; }
+  .page-title-block .page-title-input { padding-left: 0; }
   .editor-statusbar { left: 0; }
 
   /* ── View Tabs ── */
@@ -3738,6 +3761,9 @@ button.breadcrumb-current { max-width: 260px; }
   .page-title-input { font-size: 22px; }
   .blocks-container { padding: 6px 12px 80px; }
   .page-icon-emoji { font-size: 28px; }
+  .page-title-block::before { display: none; }
+  .page-title-block .page-icon-emoji { margin-left: 0; }
+  .page-title-block .page-title-input { padding-left: 0; }
 
   .kanban-column {
     min-width: 92vw;