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/screenshot.html

@@ -0,0 +1,22 @@
+{{ if .Get "src" }}
+  {{ $image := .Page.Resources.GetMatch (printf "*%s*" (.Get "src")) }}
+  <figure{{ with .Get "class" }} class="{{ . }}"{{ end }}>
+    {{- if .Get "href" -}}
+      <a href="{{ .Get "href" }}">
+    {{- end -}}
+    <img src="{{ $image.RelPermalink }}"
+      {{- if or (.Get "alt") (.Get "caption") }}
+        alt="{{ with .Get "alt" }}{{ . }}{{ else }}{{ .Get "caption" | markdownify | plainify }}{{ end }}"
+      {{- end -}}
+      width="100%"
+      height="auto"
+      style="max-width:{{ div $image.Width 2 }}px; max-height:{{ div $image.Height 2 }}px;"
+    />
+    {{- if .Get "href" }}</a>{{ end -}}
+    {{- if .Get "caption" -}}
+      <figcaption>
+        {{- .Get "caption" | markdownify -}}
+      </figcaption>
+    {{- end }}
+  </figure>
+{{ end }}