feat(learn): add standalone /learn pages backed by Page Data

Serve lightweight child/parent learning assistant pages at /learn without
MindSpace injection, with a rebuild script and Portal static route.

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

scripts/patch-learn-route-143.py

@@ -0,0 +1,42 @@
+#!/usr/bin/env python3
+from pathlib import Path
+
+p = Path("/Users/john/Project/Memind/server.mjs")
+text = p.read_text()
+if '"/learn"' in text and "public/learn" in text:
+    print("ALREADY_PATCHED")
+    raise SystemExit(0)
+
+needle = """  app2.use(
+    "/assets",
+    staticMiddleware(
+      pathApi.join(h5Root, "public/assets"),
+      { maxAge: "1d" }
+    )
+  );
+  app2.get(
+    "/dev/wechat-share-preview","""
+
+insert = """  app2.use(
+    "/assets",
+    staticMiddleware(
+      pathApi.join(h5Root, "public/assets"),
+      { maxAge: "1d" }
+    )
+  );
+  app2.use(
+    "/learn",
+    staticMiddleware(
+      pathApi.join(h5Root, "public/learn"),
+      { maxAge: "5m", index: "index.html" }
+    )
+  );
+  app2.get(
+    "/dev/wechat-share-preview","""
+
+if needle not in text:
+    print("NEEDLE_NOT_FOUND")
+    raise SystemExit(1)
+
+p.write_text(text.replace(needle, insert, 1))
+print("PATCHED_OK")