peek panels: reusable editor module — shared _page_editor_content.html + embed template

Architecture for zero code duplication:
- Extract page editor HTML into _page_editor_content.html (shared include)
- page_editor.html includes it (same behavior as before)
- page_editor_embed.html includes it with empty topbar (no header in peek)
- board.py: ?embed=1 renders page_editor_embed.html

Peek panels now load /pages/{id}?embed=1 in iframe:
- Editor renders without sidebar or header breadcrumb/actions
- Full editing capability (blocks, markdown, slash commands, save)
- Same code — one change to _page_editor_content.html updates everywhere

app/templates/library.html

@@ -446,13 +446,8 @@
           </div>
         </div>
       </div>
-      <div class="peek-body">
-        <div x-show="peekLoading" class="peek-loading">Loading…</div>
-        <div x-show="!peekLoading && peekContent" x-html="peekContent"></div>
-        <div x-show="!peekLoading && !peekContent" class="peek-empty">
-          <div style="margin-bottom:8px;">{{ fd_icon("file",32) }}</div>
-          <div style="font-size:14px;color:var(--text-secondary);">No preview available</div>
-        </div>
+      <div class="peek-body" style="flex:1;display:flex;flex-direction:column;">
+        <iframe id="lib-peek-iframe" src="" style="width:100%;height:100%;border:none;flex:1;"></iframe>
       </div>
     </div>
   </template>
@@ -1203,40 +1198,15 @@ function libraryPage() {
     // ── Side peek ──
     async openPeek(item) {
       this.peekItem = item;
-      this.peekContent = '';
-      this.peekLoading = true;
       this.peekFavorited = item.favorited || false;
-      try {
-        var r = await fetch('/board/api/pages/' + item.id);
-        var d = await r.json();
-        var content = d.content || '';
-        // Simple preview
-        if (d.content_format === 'blocks') {
-          try {
-            var blocks = typeof content === 'string' ? JSON.parse(content) : content;
-            var preview = '';
-            var lines = Array.isArray(blocks) ? blocks.slice(0, 30) : ((blocks && blocks.blocks) ? blocks.blocks.slice(0, 30) : []);
-            for (var i = 0; i < lines.length; i++) {
-              var b = lines[i];
-              var txt = b.content || b.text || (typeof b === 'string' ? b : '');
-              if (txt && txt.trim()) preview += '<div style="margin-bottom:6px;font-size:14px;line-height:1.5;color:var(--text-primary);">' + this._escHtml(String(txt)) + '</div>';
-            }
-            this.peekContent = preview || '<div style="color:var(--text-dim);">(empty page)</div>';
-          } catch(e) {
-            this.peekContent = '<pre style="font-size:13px;color:var(--text-primary);white-space:pre-wrap;">' + this._escHtml(String(content).substring(0, 2000)) + '</pre>';
-          }
-        } else {
-          this.peekContent = content ? '<div style="font-size:14px;line-height:1.6;color:var(--text-primary);white-space:pre-wrap;">' + this._escHtml(String(content).substring(0, 2000)) + '</div>' : '';
-        }
-      } catch(e) {
-        this.peekContent = '';
-      }
-      this.peekLoading = false;
+      var iframe = document.getElementById('lib-peek-iframe');
+      if (iframe) iframe.src = '/pages/' + item.id + '?embed=1';
     },
 
     closePeek() {
       this.peekItem = null;
-      this.peekContent = '';
+      var iframe = document.getElementById('lib-peek-iframe');
+      if (iframe) iframe.src = '';
     },
 
     async toggleFavoritePeek() {