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>

tools/docgen/gen.py

@@ -161,10 +161,10 @@ NS_TIP = {"Screen": "The 2D drawing surface.", "Color": "The named color palette
 # ---------------------------------------------------------------------------
 # shared chrome
 # ---------------------------------------------------------------------------
-def nav_html(cfg, active=None):
+def nav_html(cfg, links=None, cta_href="api.html"):
     out = []
-    for n in cfg["nav_links"]:
-        cls = 'class="nav-cta" ' if n.get("href") == "api.html" else ""
+    for n in (links if links is not None else cfg["nav_links"]):
+        cls = 'class="nav-cta" ' if n.get("href") == cta_href else ""
         out.append('<a %shref="%s">%s</a>' % (cls, n["href"], esc(n["label"])))
     return "".join(out)
 
@@ -186,10 +186,12 @@ def head_html(title, desc, css_file):
 </head>""", {"TITLE": esc(title), "DESC": escattr(desc), "CSS": css})
 
 def topbar(cfg):
+    refnav = nav_html(cfg, links=cfg.get("ref_nav_links", cfg["nav_links"]), cta_href=None) \
+        + '<a class="nav-cta" href="%s">Source ↗</a>' % cfg["repo_url"]
     return ('<header class="nav"><div class="wrap nav-in">'
             '<a class="brand" href="index.html"><span class="logo">L</span> %s</a>'
             '<button class="nav-toggle" aria-label="Toggle menu" aria-expanded="false">☰</button>'
-            '<nav class="nav-links">%s</nav></div></header>') % (esc(cfg["brand"]), nav_html(cfg))
+            '<nav class="nav-links">%s</nav></div></header>') % (esc(cfg["brand"]), refnav)
 
 # ---------------------------------------------------------------------------
 # per-item page