feat: sidebar tree dynamically refreshes after CRUD in local-workspace

- New endpoint GET /api/sidebar/workspace-tree returns sidebar tree HTML fragment
- refreshSidebarTree() in appState() fetches and replaces #sidebar-workspace-items
- Custom event 'flowdeck:sidebar-refresh' dispatched after doCreate/doRename/doDelete
- newFolderInWorkspace, deleteWorkspacePage, wsCtxAction('rename') now use
  refreshSidebarTree() instead of window.location.reload()
- Sidebar stays in sync without full page refresh

app/routers/dashboard.py

@@ -1507,3 +1507,63 @@ async def update_account(request: Request):
     response = JSONResponse({"status": "ok", "user": {k: user_data[k] for k in ("id","login","full_name","email","is_admin")}})
     response.set_cookie("flowdeck_session", new_session, httponly=True, max_age=86400 * 7, samesite="lax", path="/")
     return response
+
+
+# ═══════════ Sidebar Refresh API ═══════════
+
+@router.get("/api/sidebar/workspace-tree")
+async def sidebar_workspace_tree(request: Request):
+    """Return the sidebar workspace tree as HTML fragment.
+    
+    Called by appState().refreshSidebarTree() after CRUD operations
+    in the main content area to keep the sidebar in sync.
+    """
+    from jinja2 import Environment, FileSystemLoader
+    from app.routers.board import _load_workspace_pages
+    
+    user = SessionManager.decode_session(request.cookies.get("flowdeck_session", ""))
+    if not user:
+        return HTMLResponse("")
+    
+    ws_cookie = request.cookies.get("flowdeck_workspace", "")
+    if not ws_cookie:
+        return HTMLResponse('<li class="sidebar-item empty-hint"><span class="page-icon">📄</span><span class="page-name text-dim">No pages yet</span></li>')
+    
+    # Gitea workspace — no server-side tree, loaded client-side
+    if ws_cookie.startswith("gitea:"):
+        return HTMLResponse('<li class="sidebar-item empty-hint"><span class="page-icon">🔗</span><span class="page-name text-dim">Remote workspace</span></li>')
+    
+    try:
+        ws_id = int(ws_cookie)
+        with get_conn() as conn:
+            # Verify workspace belongs to user
+            row = conn.execute(
+                "SELECT id FROM workspaces WHERE id=? AND owner_id=?",
+                (ws_id, user["id"])
+            ).fetchone()
+            if not row:
+                return HTMLResponse(
+                    '<li class="sidebar-item empty-hint"><span class="page-icon">📄</span>'
+                    '<span class="page-name text-dim">No pages yet</span></li>'
+                )
+        
+        pages = _load_workspace_pages(ws_cookie)
+        if not pages:
+            return HTMLResponse(
+                '<li class="sidebar-item empty-hint"><span class="page-icon">📄</span>'
+                '<span class="page-name text-dim">No pages yet</span></li>'
+            )
+        
+        # Render the tree using the same Jinja2 macro as base.html
+        env = Environment(loader=FileSystemLoader("app/templates"))
+        template = env.from_string(
+            "{% from 'base.html' import render_workspace_tree %}"
+            "{{ render_workspace_tree(pages) }}"
+        )
+        html = template.render(pages=pages)
+        return HTMLResponse(html)
+    except (ValueError, Exception):
+        return HTMLResponse(
+            '<li class="sidebar-item empty-hint"><span class="page-icon">📄</span>'
+            '<span class="page-name text-dim">No pages yet</span></li>'
+        )