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/ui/vendor/whynot-design/tokens/index.json

@@ -0,0 +1,6 @@
+{
+  "comment": "Manifest pointing at the three token files. Source-of-truth for any future Style Dictionary build.",
+  "colors":  "./colors.json",
+  "type":    "./type.json",
+  "spacing": "./spacing.json"
+}