release: v0.4.0 site/README consistency + Web 1.0 re-skin

- Docs site: drop jekyll-theme-cayman for a hand-rolled _layouts/default.html
  (masthead band + middot text nav + footer with last-updated stamp and legal
  line; head re-plumbed with {% seo %}, viewport, favicon); head-custom.html
  fully rewritten to the chosen design tokens - charcoal/off-white/amber,
  Libre Baskerville headings over system sans, square corners, 1px borders,
  flat (no gradients/shadows), mermaid wrapper re-skinned.
- docs/index.md: v0.4.0 status (native widescreen, aim system, rebinding,
  crosshair, rumble, rebuilt overlay); Honest status replaced by the v0.4.0
  release-notes known issues; body anchor-nav line; legal footer moved to
  layout.
- security-and-fidelity-status.md: front matter so {% seo %} titles it.
- README.md: v0.4.0 truth pass (status, Working/Known issues, Deck preset
  2x MSAA / 250% per code, background stats 981 commits / 283 findings,
  comparison table, GEPD-default controls paragraph, earlier builds) plus
  markdown-native motifs matching the site: top anchor-nav line, --- section
  rules, last-updated footer stamp, license badge in the amber accent.
- release-notes: SFTP sideload mention (leftover from the Deck session).

.github/release-notes.md

@@ -282,7 +282,7 @@ to install.
    `prepare-assets/ge007-convert` inside the bundle; you can also run it
    manually; it prints what it's doing.)
 
-**Steam Deck:** sideload the unpacked folder (USB or a file manager), do
+**Steam Deck:** sideload the unpacked folder (SFTP, USB or a file manager), do
 steps 2–3, then add the executable to Games → *Add Game* as a non-Steam
 game. The first launch in Game Mode picks up the Deck preset (native
 1280×800, 2× MSAA, vsync) automatically if no config exists yet.