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/js/mermaid.js

@@ -0,0 +1,33 @@
+function css(name) {
+  return "rgb(" + getComputedStyle(document.documentElement).getPropertyValue(name) + ")";
+}
+
+function initMermaidLight() {
+  mermaid.initialize({
+    theme: "base",
+    themeVariables: {
+      background: css("--color-neutral"),
+      primaryColor: css("--color-primary-200"),
+      secondaryColor: css("--color-secondary-200"),
+      tertiaryColor: css("--color-neutral-100"),
+      primaryBorderColor: css("--color-primary-400"),
+      secondaryBorderColor: css("--color-secondary-400"),
+      tertiaryBorderColor: css("--color-neutral-400"),
+      lineColor: css("--color-neutral-600"),
+      fontFamily:
+        "ui-sans-serif,system-ui,-apple-system,BlinkMacSystemFont,segoe ui,Roboto,helvetica neue,Arial,noto sans,sans-serif",
+      fontSize: "16px",
+    },
+  });
+}
+
+function initMermaidDark() {
+  mermaid.initialize({
+    theme: "dark",
+    themeVariables: {
+      fontFamily:
+        "ui-sans-serif,system-ui,-apple-system,BlinkMacSystemFont,segoe ui,Roboto,helvetica neue,Arial,noto sans,sans-serif",
+      fontSize: "16px",
+    },
+  });
+}