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.

assets/icons/keyoxide.svg

@@ -0,0 +1,16 @@
+<svg width="1024" height="1024" viewBox="0 0 1024 1024" xmlns="http://www.w3.org/2000/svg">
+  <path fill="currentColor" d="M512 11.375a500.25 500.25 0 1 0 0 1001.25 500.25 500.25 0 0 0 0-1001.25z" mask="url(#cutout)"/>
+  <defs>
+    <mask id="cutout">
+      <rect width="1024" height="1024" fill="white"/>
+      <g fill="black">
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+        <path d="M464 508.6l245.3 163.5c44.1 29.4 56 89 26.6 133.1-29.4 44.1-89 56-133.1 26.6l-288-192C288 622.1 272 592.1 272 560V336c0-53 43-96 96-96s96 43 96 96z"/>
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+        <circle cx="536" cy="119.9" r="22.2"/>
+        <circle cx="475.6" cy="103.6" r="15.5"/>
+        <circle cx="712.9" cy="250.5" r="27.2"/>
+      </g>
+    </mask>
+  </defs>
+</svg>