Unify nav across all pages; broaden safety section

- about, terms, enterprise_terms now all import and use shared nav()
- Any future nav change propagates everywhere automatically
- Remove Docs from nav (no docs yet)
- Safety: Hard Bell is for everyone, not just children - reframe copy,
  update cards and bottom callout to reflect universal applicability

src/terms.el

@@ -2,9 +2,10 @@
 // Returns complete HTML using the shared page shell from styles.el.
 
 from styles import { page_open, page_close }
+from nav    import { nav }
 
 fn terms_page() -> String {
-    return page_open() + terms_body() + page_close()
+    return page_open() + nav() + terms_body() + page_close()
 }
 
 fn terms_body() -> String {