docs(site): vertical pipeline on mobile, click tooltips, consistent chrome

- Pipeline diagram stacks vertically with downward arrows on mobile (row on
  >=720px) instead of the awkward wrap.
- Tooltip cards now open on CLICK (works on touch too), the card itself is
  clickable and opens the symbol's page in a NEW TAB, and an outside click or
  Escape closes it. Replaces the hover-only behavior.
- Reference pages get their own nav — Home / API Reference / Source ↗ — instead
  of the landing-only Features/Examples/Get started anchors, and now include the
  Source link.
- Unify the container width (1120px) across the landing and all reference pages
  so the header and content align between them.
- Reword extern/@export FFI docs from "C-ABI" to "native" for consistency with
  the site's no-C wording.

Verified in-browser at 375px and 1280px: vertical pipeline, click→card→new-tab,
outside-click close, correct reference nav, aligned container; 158 examples still
compile.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/site/site.json

@@ -14,6 +14,10 @@
     { "label": "Get started", "href": "#start" },
     { "label": "API Reference", "href": "api.html" }
   ],
+  "ref_nav_links": [
+    { "label": "Home", "href": "index.html" },
+    { "label": "API Reference", "href": "api.html" }
+  ],
   "hero": {
     "pill": "Opinionated · Batteries-included · No framework",
     "title_pre": "Build a game,",