feat: split Ordo designer into library monorepo

Extract ordo-designer-vue package with shadcn UI and context-based state; add playground app, library-api docs, and README.

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/playground/index.html

@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <link rel="icon" href="/favicon.ico" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>Ordo Designer Playground</title>
+  </head>
+  <body>
+    <div id="app"></div>
+    <script type="module" src="/src/main.ts"></script>
+  </body>
+</html>