website: the two-tone headings are back, and the home page's sections are ruled apart

Two notes from the operator, 2026-10-12: the white/blue heading split was lost
in the M3 switch and should return everywhere, the apps page categories
included; and the home page's sections ran into one another.

- 41 headings get their <span> back (home 5+5, apps 6+6, FAQ 6+7, services 3+3).
  The style never went away - site.css has styled `h2 span` blue all along; the
  M3 rewrite dropped the markup. No text changed: the span wraps words that were
  already there. The three home headings that predate M3 are split where they
  were split then.
- Apps and FAQ categories are new to the treatment: a name with an & splits
  there, a phrase on its last words. Five one-word headings stay plain.
- The home page's sections get a 1px --line rule with 2.75rem of air on each
  side, so it sits centred in the gap; the first also parts the hero from the
  page. Home page only.
- Blue on the page background measures 7.9:1 - AA at any size.
- site.css ?v=28.

website/en/technology.html

@@ -41,7 +41,7 @@
     <link rel="preload" as="font" type="font/woff2" crossorigin href="/assets/fonts/pjs-latin.woff2">
     <link rel="preload" as="font" type="font/woff2" crossorigin href="/assets/fonts/pjs-latin-ext.woff2">
     <!-- shared assets: bump ?v= together on any site.css/icons.svg change -->
-    <link rel="stylesheet" href="/assets/site.css?v=27">
+    <link rel="stylesheet" href="/assets/site.css?v=28">
     <link rel="stylesheet" href="/assets/shell.css?v=25">
     <link rel="icon" type="image/png" href="/assets/logo_favicon_2.svg">
     <script defer src="/assets/gallery.js?v=2"></script>