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/accordion.html

@@ -0,0 +1,55 @@
+{{ $id := delimit (slice "accordion" (partial "functions/uid.html" .)) "-" }}
+{{ $mode := .Get "mode" | default "collapse" }}
+{{ $separated := .Get "separated" | default false }}
+{{ $isSeparated := or (eq $separated true) (eq $separated "true") }}
+
+<div
+  id="{{ $id }}"
+  class="{{ if $isSeparated }}space-y-2{{ else }}border border-neutral-200 dark:border-neutral-700 rounded-lg overflow-hidden{{ end }}"
+  data-accordion="{{ $mode }}"
+  data-accordion-separated="{{ $isSeparated }}"
+>
+  {{- .Inner -}}
+</div>
+{{ if $isSeparated }}
+<style>
+  #{{ $id }} > details + details {
+    margin-top: 0.5rem;
+  }
+</style>
+{{ else }}
+<style>
+  #{{ $id }} > details + details {
+    border-top: 1px solid rgb(var(--color-neutral-200));
+  }
+  .dark #{{ $id }} > details + details {
+    border-top-color: rgb(var(--color-neutral-700));
+  }
+</style>
+{{ end }}
+<style>
+  #{{ $id }} details[data-accordion-item] > summary .accordion-chevron {
+    transform: rotate(-90deg);
+    transition: transform 200ms ease-in-out;
+  }
+  #{{ $id }} details[data-accordion-item][open] > summary .accordion-chevron {
+    transform: rotate(0deg);
+  }
+</style>
+{{ if eq $mode "collapse" }}
+<script>
+  (() => {
+    const root = document.getElementById("{{ $id }}");
+    if (!root) return;
+    const items = root.querySelectorAll("details[data-accordion-item]");
+    items.forEach((item) => {
+      item.addEventListener("toggle", () => {
+        if (!item.open) return;
+        items.forEach((other) => {
+          if (other !== item) other.removeAttribute("open");
+        });
+      });
+    });
+  })();
+</script>
+{{ end }}