Integrate whynot-design into Economic Observatory UI

Vendor whynot-design Layer 1 (tokens, CSS) and Layer 2 (<wn-*>
components) via scripts/sync-whynot-design.sh with a pinned ref.
Migrate the observatory shell to canonical web components, keep
observatory-specific layout in styles.css, and add vendor integrity
tests plus correct JS MIME types on the dev server.

projects/coulomb-pricing/tests/test_ui_vendor.py

@@ -0,0 +1,62 @@
+from __future__ import annotations
+
+import importlib
+import threading
+from http.server import HTTPServer
+from pathlib import Path
+
+import pytest
+
+ROOT = Path(__file__).resolve().parent.parent
+VENDOR = ROOT / "ui" / "vendor" / "whynot-design"
+
+REQUIRED_VENDOR_FILES = [
+    VENDOR / ".whynot-design-ref",
+    VENDOR / "colors_and_type.css",
+    VENDOR / "components.css",
+    VENDOR / "index.js",
+    VENDOR / "elements" / "atoms.js",
+    VENDOR / "elements" / "chrome.js",
+    VENDOR / "elements" / "form.js",
+    VENDOR / "elements" / "layout.js",
+    VENDOR / "elements" / "icons.js",
+    VENDOR / "elements" / "_styles.js",
+    VENDOR / "tokens" / "colors.json",
+]
+
+
+def test_vendor_tree_is_complete() -> None:
+    missing = [path for path in REQUIRED_VENDOR_FILES if not path.exists()]
+    assert not missing, f"Missing vendored whynot-design files: {missing}"
+
+
+def test_vendor_ref_is_pinned() -> None:
+    ref = (VENDOR / ".whynot-design-ref").read_text(encoding="utf-8").strip()
+    assert len(ref) == 40
+
+
+def test_server_serves_vendor_modules() -> None:
+    server_module = importlib.import_module("observatory.server")
+    handler = server_module.ObservatoryHandler
+    handler.data_dir = ROOT / "data"
+
+    httpd = HTTPServer(("127.0.0.1", 0), handler)
+    port = httpd.server_address[1]
+    thread = threading.Thread(target=httpd.serve_forever, daemon=True)
+    thread.start()
+
+    try:
+        import urllib.request
+
+        index = urllib.request.urlopen(f"http://127.0.0.1:{port}/", timeout=2)
+        assert "wn-top-nav" in index.read().decode("utf-8")
+
+        module = urllib.request.urlopen(
+            f"http://127.0.0.1:{port}/ui/vendor/whynot-design/index.js",
+            timeout=2,
+        )
+        assert module.headers["Content-Type"].startswith("application/javascript")
+        assert "defineAtoms" in module.read().decode("utf-8")
+    finally:
+        httpd.shutdown()
+        thread.join(timeout=2)