seo: full audit fixes — meta, og, schema, canonical, sitemap, headings, alts

- Per-page title/description/canonical/OG tags: about, checkout (per-plan),
  terms, enterprise-terms, success all get unique SEO blocks
- Homepage title updated to em-dash form; meta description adds CTA
- og:site_name added to all pages
- noindex/nofollow on checkout, success, account pages
- Sitemap (/sitemap.xml) with all public pages; robots.txt updated with
  Sitemap directive and Disallow for private paths
- Schema: WebSite type added, Organization gains logo ImageObject, SoftwareApplication
  gains url field, billingIncrement corrected to billingPeriod (ISO 8601 P1M),
  sameAs gains x.com/neurontechai alongside GitHub
- marked.min.js given defer attribute (was render-blocking)
- page_head refactored into page_head_base + page_seo_block + page_open_seo
  for clean inner-page overrides without duplicating the CSS/script block

src/enterprise_terms.el

@@ -1,7 +1,7 @@
 // components/enterprise_terms.el - Enterprise Agreement page.
 // Returns complete HTML using the shared page shell from styles.el.
 
-from styles import { page_open, page_close }
+from styles import { page_open_seo, page_close }
 from nav    import { nav }
 
 extern fn el_div(attrs: String, children: String) -> String
@@ -15,7 +15,13 @@ extern fn el_li(attrs: String, children: String) -> String
 extern fn el_em(children: String) -> String
 
 fn enterprise_terms_page() -> String {
-    page_open() + enterprise_terms_body() + page_close()
+    page_open_seo(
+        "Enterprise Agreement — Neuron",
+        "The Neuron Enterprise Agreement governs enterprise deployments of Neuron software. Review licensing terms, data handling, and compliance provisions.",
+        "/legal/enterprise-terms",
+        "The Neuron Enterprise Agreement — governing enterprise deployments, licensing, data handling, and compliance.",
+        "false"
+    ) + enterprise_terms_body() + page_close()
 }
 
 fn et_section(num: String, title: String, body: String) -> String {