SX docs: configurable shell, SX-native event handlers, nav fixes

- Configurable page shell (~sx-page-shell kwargs + SX_SHELL app config)
  so each app controls its own assets — sx docs loads only sx-browser.js
- SX-evaluated sx-on:* handlers (eval-expr instead of new Function)
  with DOM primitives registered in PRIMITIVES table
- data-init boot mode for pure SX initialization scripts
- Jiggle animation on links while fetching
- Nav: 3-column grid for centered alignment, is-leaf sizing,
  fix map-indexed param order (index, item), guard mod-by-zero
- Async route eval failure now falls back to server fetch
  instead of silently rendering nothing
- Remove duplicate h1 title from ~doc-page
- Re-bootstrap sx-ref.js + sx-browser.js

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

sx/app.py

@@ -67,6 +67,34 @@ def create_app() -> "Quart":
         **extra_kw,
     )
 
+    # Minimal shell — no Prism, no SweetAlert, no body.js
+    # sx docs uses custom highlight.py, not Prism; body.js is for legacy apps
+    app.config["SX_SHELL"] = {
+        "head_scripts": [],  # no CDN scripts
+        "body_scripts": [],  # no body.js
+        "inline_head_js": "",  # no pre-boot JS (hover-capable, close-details unused)
+        "inline_css": (
+            ".sx-indicator{display:none}"
+            ".sx-request .sx-indicator{display:inline-flex}"
+            "@keyframes sxJiggle{0%,100%{transform:translateX(0)}"
+            "25%{transform:translateX(-.5px)}75%{transform:translateX(.5px)}}"
+            "a.sx-request{animation:sxJiggle .3s ease-in-out infinite}"
+        ),
+        # Nav link aria-selected update on client-side routing — pure SX
+        "init_sx": (
+            '(dom-listen (dom-body) "sx:clientRoute"'
+            '  (fn (e)'
+            '    (let ((p (get (event-detail e) "pathname")))'
+            '      (when p'
+            '        (for-each'
+            '          (fn (a) (dom-set-attr a "aria-selected" "false"))'
+            '          (dom-query-all "nav a[aria-selected]"))'
+            '        (for-each'
+            '          (fn (a) (dom-set-attr a "aria-selected" "true"))'
+            '          (dom-query-all (str "nav a[href=\\"" p "\\"]")))))))'
+        ),
+    }
+
     from sxc.pages import setup_sx_pages
     setup_sx_pages()