migrate to decoupled Blowfish layout, fix TOC scrollspy, and update docs

- Theme Decoupling & Cleanup:
      - Fully decoupled and vendored the Blowfish theme directly into root directories (layouts/,
  assets/, static/, data/, i18n/).
      - De-registered and cleaned up legacy Git submodules (themes/blowfish, themes/hugo-admonitions)
  from the Git index to protect the build from upstream breakages.
      - Configured .gitignore to ignore development preview symlinks (content, static,
  config/_default/menus.en.toml), build folders (public/, resources/), and locks.

    - TOC & Layout Fixes:
      - Replaced the custom layouts/_default/single.html template with the Blowfish default to restore
  native container widths and the side-by-side flex layout.
      - Restored TOC to float on the right sidebar on desktop viewports and render inline on mobile
  viewports.
      - Fixed a parameter resolution bug in layouts/partials/toc.html by checking both .Site.Params.
  smartTOC and .Site.Params.article.smartTOC (where it is defined in params.toml).
      - Upgraded the TOC scrollspy JavaScript to target all '#TableOfContents' containers on the page,
  enabling highlight tracking on both desktop and mobile layouts.

    - Documentation Updates (README.md):
      - Restored YAML front matter metadata block at the top.
      - Added detailed notes on the CI/CD build process and Gitea runner deployment targets
  (/srv/www/docs-public and /srv/www/docs-private).
      - Added a categorized and sorted "Shortcodes Quick Reference" table at the top of the shortcodes
  section (ordered by Custom, Hugo Default, and Blowfish).
      - Documented custom shortcodes (Include, Screenshot, Raw HTML) and missing Hugo default
  shortcodes (Highlight, Instagram, Param, Ref, Relref, Twitter, Vimeo, Youtube).
      - Restructured headings to ensure all sub-shortcodes are H3, removed block break tags (<br/>),
  and appended horizontal separators (---) after H2 sections.

layouts/_default/_markup/render-link.html

@@ -0,0 +1,38 @@
+{{/* From Hugo, Apache v2 license
+  https://github.com/gohugoio/hugo/blob/master/tpl/tplimpl/embedded/templates/_markup/render-link.html
+*/}}
+{{- $u := urls.Parse .Destination -}}
+{{- $href := $u.String -}}
+{{- if strings.HasPrefix $u.String "#" -}}
+  {{- $href = printf "%s#%s" .PageInner.RelPermalink $u.Fragment -}}
+{{- else if and $href (not $u.IsAbs) -}}
+  {{- $path := strings.TrimPrefix "./" $u.Path -}}
+  {{- with or
+    ($.PageInner.GetPage $path)
+    ($.PageInner.Resources.Get $path)
+    (resources.Get $path)
+  -}}
+    {{- $href = .RelPermalink -}}
+    {{- with $u.RawQuery -}}
+      {{- $href = printf "%s?%s" $href . -}}
+    {{- end -}}
+    {{- with $u.Fragment -}}
+      {{- $href = printf "%s#%s" $href . -}}
+    {{- end -}}
+  {{- end -}}
+{{- end -}}
+
+{{/* Open external links in a new tab if
+  configured to do so by the page param externalLinkForceNewTab
+  or site param article.externalLinkForceNewTab
+  and the link starts with http: or https:
+*/}}
+{{- $forceNewTab := .Page.Params.externalLinkForceNewTab | default (.Page.Site.Params.article.externalLinkForceNewTab | default true) -}}
+{{- $isExternal := or (strings.HasPrefix .Destination "http:") (strings.HasPrefix .Destination "https:") -}}
+{{- $newTab := and $forceNewTab $isExternal -}}
+
+<a href="{{ $href }}" {{ with .Title }}title="{{ . }}"{{ end }}
+  {{- if $newTab }} target="_blank" rel="noreferrer"{{ end }}>
+  {{- .Text | safeHTML -}}
+</a>
+{{- /* Trim EOF */ -}}