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/rss.xml

@@ -0,0 +1,55 @@
+{{- $pctx := . -}}
+{{- if .IsHome -}}{{ $pctx = .Site }}{{- end -}}
+{{- $pages := slice -}}
+{{- if or $.IsHome $.IsSection -}}
+{{- $pages = $pctx.RegularPages -}}
+{{- else -}}
+{{- $pages = $pctx.Pages -}}
+{{- end -}}
+{{- $limit := .Site.Config.Services.RSS.Limit -}}
+{{- if ge $limit 1 -}}
+{{- $pages = $pages | first $limit -}}
+{{- end -}}
+{{- printf "<?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"yes\"?>" | safeHTML }}
+<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">
+  <channel>
+    <title>{{ if eq  .Title  .Site.Title }}{{ .Site.Title }}{{ else }}{{ with .Title }}{{.}} on {{ end }}{{ .Site.Title }}{{ end }}</title>
+    <link>{{ .Permalink }}</link>
+    <description>Recent content {{ if ne  .Title  .Site.Title }}{{ with .Title }}in {{.}} {{ end }}{{ end }}on {{ .Site.Title }}</description>
+    <generator>Hugo -- gohugo.io</generator>
+    <language>{{ site.Language.Locale }}</language>{{ with .Site.Params.Author.email }}
+    <managingEditor>{{.}}{{ with $.Site.Params.Author.name }} ({{.}}){{end}}</managingEditor>{{end}}{{ with .Site.Params.Author.email }}
+    <webMaster>{{.}}{{ with $.Site.Params.Author.name }} ({{.}}){{end}}</webMaster>{{end}}
+    {{ if .Site.Params.footer.showCopyright | default true -}}
+    <copyright>{{ with replace .Site.Params.copyright "{ year }" now.Year }}{{.}}{{ else }}© {{ now.Format "2006" }} {{ .Site.Params.Author.name }}{{- end }}</copyright>
+    {{- end }}
+    {{ if not .Date.IsZero }}<lastBuildDate>{{ (index $pages.ByLastmod.Reverse 0).Lastmod.Format "Mon, 02 Jan 2006 15:04:05 -0700" | safeHTML }}</lastBuildDate>{{ end }}
+    {{- with .OutputFormats.Get "RSS" -}}
+    {{ printf "<atom:link href=%q rel=\"self\" type=%q />" .Permalink .MediaType | safeHTML }}
+    {{- end -}}
+    {{ if and (.Site.Params.rssnext.feedId) (.Site.Params.rssnext.userId) }}
+    <follow_challenge>
+      <feedId>{{ .Site.Params.rssnext.feedId }}</feedId>
+      <userId>{{ .Site.Params.rssnext.userId }}</userId>
+    </follow_challenge>
+    {{ end }}
+    {{ range $pages }}
+    <item>
+      <title>{{ .Title }}</title>
+      <link>{{ .Permalink }}</link>
+      <pubDate>{{ .Date.Format "Mon, 02 Jan 2006 15:04:05 -0700" | safeHTML }}</pubDate>
+      {{ with .Site.Params.Author.email }}<author>{{.}}{{ with $.Site.Params.Author.name }} ({{.}}){{end}}</author>{{end}}
+      <guid>{{ .Permalink }}</guid>
+      <description>{{ .Summary | transform.XMLEscape | safeHTML }}</description>
+      {{ range ( where .Site.RegularPages ".RelPermalink" .RelPermalink | first 1 ) }}
+        {{- $images := .Resources.ByType "image" -}}
+        {{- $featured := $images.GetMatch "*feature*" -}}
+        {{- if not $featured }}{{ $featured = $images.GetMatch "{*cover*,*thumbnail*}" }}{{ end -}}
+        {{- with $featured -}}
+        <media:content xmlns:media="http://search.yahoo.com/mrss/" url="{{ $featured.Permalink  }}" />
+        {{- end -}}
+      {{ end }}
+    </item>
+    {{ end }}
+  </channel>
+</rss>