Fix <sql> silent-failure bug; split /vst into overview + subpage; misc site fixes

- __mysql.cpp: <sql> never checked mysql_real_query's own return code,
  so a genuine query failure was indistinguishable from "ran fine, zero
  rows" - <try>/<catch> around a failing <sql> never actually caught
  anything anywhere. Now throws on a real failure.
- spa.js: dynamically re-injected scripts now run in true sequential
  order (wait for each external script's load event before running the
  next), fixing checkout's Square card field never building on the
  first client-side navigation to /checkout (only after a refresh) -
  async=false alone only orders multiple external scripts relative to
  each other, it doesn't delay a plain inline sibling.
- /vst split into a real overview + /vst/modular1 subpage with a left
  menu, reusing opensource.page's existing subpage-tier pattern
  (opensource.menu/main.css's submenuitem-active highlighting, and
  several other subpage-tier retirements, were already finished earlier
  this session but never committed - included here too).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

jetc/barant-site/assets/images/spa.js

@@ -127,19 +127,43 @@
     // a client-side SPA swap (e.g. clicking "Check Out") instead of a
     // full reload; only worked by accident on a fresh /checkout load.
     // Re-creating each script element makes the browser actually run
-    // it. async=false on src="" ones preserves normal in-order
-    // execution (dynamically-inserted external scripts default to
-    // async otherwise), matching how a real page load would run them.
+    // it. A prior fix set async=false on src="" ones, but that only
+    // orders MULTIPLE external scripts relative to each other - it
+    // does nothing to delay a plain inline script sitting right after
+    // one, which still runs immediately on insertion regardless of a
+    // sibling's in-flight fetch. checkout.page is exactly that shape
+    // (an external Square SDK <script src> immediately followed by an
+    // inline script calling Square.payments(...)): on a client-side
+    // SPA swap the inline script ran before Square had actually
+    // finished downloading, throwing "Square is not defined" inside an
+    // async function with no visible catch, leaving the card container
+    // permanently empty - reported as "checkout's card field doesn't
+    // build the first time, only after a refresh" (a real full page
+    // load's parser-inserted <script src> blocks until loaded before
+    // the next tag runs, which a dynamically re-created one does not
+    // do on its own). Fixed by actually waiting for each external
+    // script's load/error event before moving on to the next one,
+    // rather than trusting async=false's narrower ordering guarantee -
+    // reproduced the failure and confirmed the fix against a real
+    // artificially-delayed script load before deploying.
     var scripts = content.querySelectorAll('script');
-    for (var i = 0; i < scripts.length; i++) {
-      var old = scripts[i];
+    var scriptList = [];
+    for (var i = 0; i < scripts.length; i++) scriptList.push(scripts[i]);
+    (function runScript(index) {
+      if (index >= scriptList.length) return;
+      var old = scriptList[index];
       var fresh = document.createElement('script');
       for (var j = 0; j < old.attributes.length; j++)
         fresh.setAttribute(old.attributes[j].name, old.attributes[j].value);
-      if (fresh.src) fresh.async = false;
       fresh.textContent = old.textContent;
-      old.parentNode.replaceChild(fresh, old);
-    }
+      if (fresh.src) {
+        fresh.onload = fresh.onerror = function() { runScript(index + 1); };
+        old.parentNode.replaceChild(fresh, old);
+      } else {
+        old.parentNode.replaceChild(fresh, old);
+        runScript(index + 1);
+      }
+    })(0);
     // #_spa_panelmenu carries the CURRENT page's own side-menu markup
     // (mainpagetemplate.jet renders it into every fragment response
     // specifically so this can pull it out) - extracted from the