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/language/annotations/annot-export.md

@@ -5,17 +5,17 @@ category: annotations
 kind: annotation
 tokens: @export
 sig: @export fn name(…) -> R
-tip: Expose a function as a C-ABI symbol so a host can call it.
+tip: Expose a function as a native symbol so a host can call it.
 order: 3
 ---
 
-<code>@export</code> makes a <code>fn</code> visible outside the module as a plain C-ABI symbol, so a host program or another linked object can call it by name. Without it, functions are internal to the compiled unit; with it, the emitted symbol is externally linkable, which is how Ludic hands entry points to a runtime seam or a foreign caller. It is the outbound counterpart to <code>extern fn</code>, which pulls a foreign symbol in. Keep exported signatures to POD scalars and pointers, since they cross a C boundary where Ludic's richer types do not apply.
+<code>@export</code> makes a <code>fn</code> visible outside the module as a plain native symbol, so a host program or another linked object can call it by name. Without it, functions are internal to the compiled unit; with it, the emitted symbol is externally linkable, which is how Ludic hands entry points to a runtime seam or a foreign caller. It is the outbound counterpart to <code>extern fn</code>, which pulls a foreign symbol in. Keep exported signatures to POD scalars and pointers, since they cross a native ABI boundary where Ludic's richer types do not apply.
 
 ```ludic
 program ScoreModule {
   var running_total: int = 0
 
-  @export fn add_points(amount: int) -> int {      # callable from a C-ABI host
+  @export fn add_points(amount: int) -> int {      # callable from a native host
     running_total = running_total + amount
     return running_total
   }