Adopt skainet-docs-ui v1.1.1 (#53)

Bumps docs/antora-playbook.yml ui.bundle.url from upstream
gitlab.com/antora/antora-ui-default to the new shared SKaiNET-
branded bundle at:

    https://github.com/SKaiNET-developers/skainet-docs-ui/releases/download/v1.1.1/ui-bundle.zip

The new bundle is the shared SKaiNET docs UI from
https://github.com/SKaiNET-developers/skainet-docs-ui — same
URL mainline SKaiNET pins to as of SKaiNET#502.

## Visual changes

- SKaiNET red palette (#dc2626) replaces upstream Antora blue
- Orbitron (display) + Inter (body) + Fira Code (mono) replace Roboto
- Light + dark theme toggle in the navbar (FOUC-safe inline head
  bootstrap, persisted via localStorage, prefers-color-scheme fallback)
- 6px thin custom scrollbar
- Rounded code blocks with GitHub-light / GitHub-dark backgrounds
- Primary-red focus glow on interactive elements
- New SKaiNET footer with cross-repo links to mainline +
  skainet-docs-ui (replaces the upstream Antora default UI /
  MPL-2.0 boilerplate)
- .card-grid CSS available but unused on this site (the existing
  Key Features / Supported Model Families content stays
  untouched)
- Mobile responsive (hamburger menu from upstream preserved)

## Out of scope

- Rewriting the index.adoc landing with a Diátaxis card-grid. The
  transformers landing has substantial real content (Key Features
  table, Supported Model Families table) that shouldn't be
  replaced wholesale. A future PR can add a card-grid SECTION
  above or below the existing content.
- Self-hosted fonts. v1.1.1 still loads from Google Fonts; can
  move to bundled @font-face when skainet-docs-ui v1.2 ships.
- Search wiring.

Closes #53.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: claude

docs/antora-playbook.yml

@@ -18,7 +18,12 @@ asciidoc:
 
 ui:
   bundle:
-    url: https://gitlab.com/antora/antora-ui-default/-/jobs/artifacts/HEAD/raw/build/ui-bundle.zip?job=bundle-stable
+    # SKaiNET-branded UI bundle from the shared skainet-docs-ui repo:
+    #   https://github.com/SKaiNET-developers/skainet-docs-ui
+    # Pinned to a specific tag for reproducible builds. Bumping
+    # this URL to a newer version is a one-line PR. Mainline
+    # SKaiNET pins the same bundle in its own playbook.
+    url: https://github.com/SKaiNET-developers/skainet-docs-ui/releases/download/v1.1.1/ui-bundle.zip
     snapshot: true
 
 output: