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/shortcodes/codeimporter.html

@@ -0,0 +1,27 @@
+{{ $url := .Get "url" }}
+{{ $type := .Get "type" }}
+{{ $startLine := .Get "startLine" | default 1 | int }}
+{{ $startLine = sub $startLine 1 }}
+{{ $endLine := .Get "endLine" | default -1 | int }}
+{{ $selectedLines := slice }}
+{{ with resources.GetRemote (urls.Parse $url) }}
+  {{ $lines := split .Content "\n" }}
+  {{ $totalLine := $lines | len }}
+
+  {{ if ne $endLine -1 }}
+    {{ $endLine = math.Min $endLine $totalLine }}
+  {{ else }}
+    {{ $endLine = $totalLine }}
+  {{ end }}
+
+  {{ if gt $startLine $endLine }}
+    {{ errorf "codeimporter shortcode: startLine is greater than endLine" . }}
+  {{ end }}
+
+  {{ $selectedLines := first $endLine $lines }}
+  {{ $selectedLines = after $startLine $selectedLines }}
+  {{ $codeBlock := printf "```%s\n%s\n```" $type (delimit $selectedLines "\n") }}
+  {{ $codeBlock | markdownify }}
+{{ else }}
+  {{ warnf "codeimporter shortcode: unable to fetch %q: %s" $url .Position }}
+{{ end }}