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/partials/hero/big.html

@@ -0,0 +1,76 @@
+{{ $disableImageOptimization := site.Store.Get "disableImageOptimization" }}
+
+{{ $useDefault := false }}
+{{ $featured := "" }}
+{{ $featuredURL := "" }}
+{{ with .Params.featureimage }}
+  {{ if or (strings.HasPrefix . "http:") (strings.HasPrefix . "https:") }}
+    {{ if site.Params.hotlinkFeatureImage }}
+      {{ $featuredURL = . }}
+    {{ else }}
+      {{ $featured = resources.GetRemote . }}
+    {{ end }}
+  {{ else }}
+    {{ $featured = resources.Get . }}
+  {{ end }}
+{{ end }}
+
+{{ if not (or $featured $featuredURL) }}
+  {{ $images := .Resources.ByType "image" }}
+  {{ range slice "*background*" "*feature*" "*cover*" "*thumbnail*" }}
+    {{ if not $featured }}{{ $featured = $images.GetMatch . }}{{ end }}
+  {{ end }}
+{{ end }}
+
+{{ if not (or $featured $featuredURL) }}
+  {{ $default := site.Store.Get "defaultBackgroundImage" }}
+  {{ if $default.url }}
+    {{ $featuredURL = $default.url }}
+    {{ $useDefault = true }}
+  {{ else if $default.obj }}
+    {{ $featured = $default.obj }}
+    {{ $useDefault = true }}
+  {{ end }}
+{{ end }}
+
+{{/* generate image URL if not hotlink */}}
+{{ if not $featuredURL }}
+  {{ with $featured }}
+    {{ $featuredURL = .RelPermalink }}
+    {{ if not (or $disableImageOptimization (eq .MediaType.SubType "svg")) }}
+      {{ $size := site.Store.Get "backgroundImageWidth" }}
+      {{ $featuredURL = (.Resize $size).RelPermalink }}
+    {{ end }}
+  {{ end }}
+{{ end }}
+
+{{ $caption := "" }}
+{{ if .Params.featureimagecaption }}
+  {{- $caption = .Params.featureimagecaption -}}
+{{ end }}
+
+{{- $alt := .Page.Title -}}
+{{- with .Page.Params.alt }}{{ $alt = . }}{{ end -}}
+
+{{ with $featuredURL }}
+  {{ $style := "" }}
+  {{ $defaultPosition := cond $useDefault site.Params.imagePosition false }}
+  {{ with $.Params.imagePosition | default $defaultPosition }}
+    {{ $style = printf "object-position: %s;" . }}
+  {{ end }}
+  <figure>
+    <img
+      src="{{ . }}"
+      alt="{{ $alt }}"
+      loading="eager"
+      decoding="async"
+      fetchpriority="high"
+      class="w-full rounded-lg single_hero_round nozoom"
+      {{ if $style }}style="{{ $style | safeCSS }}"{{ end }}>
+    {{ if $caption }}
+      <figcaption class="text-sm text-neutral-700 dark:text-neutral-400 hover:underline text-center">
+        {{ $caption | markdownify }}
+      </figcaption>
+    {{ end }}
+  </figure>
+{{ end }}