feat: enhance frontend Markdown rendering

- Add shared BlogMD renderer (static/js/markdown.js): marked + DOMPurify
  + highlight.js pipeline with GFM support, heading id slugger with
  CJK-aware anchors, syntax highlighting, per-block copy button and
  language badge, lazy images with lightbox, external links opened
  safely in new tabs, tables wrapped for small screens.
- Add .md-body typography styles (static/css/markdown.css) so articles,
  comments and editor previews render with proper headings, tables,
  lists, blockquotes and code blocks (previously the prose classes had
  no effect because the Tailwind typography plugin is not loaded).
- Fix marked options that were set after parsing and removed from
  marked v4+ (mangle/headerIds no-ops).
- Pin CDN versions (marked 15.0.12, dompurify 3.4.13, highlight.js
  11.12.0) instead of floating 'latest' URLs.
- Wire EasyMDE preview/side-by-side to BlogMD in admin and user
  article editors; use BlogMD for comment bodies on the article page,
  admin comment list and comment preview.
- Serve /static in main.go and deploy it in install_linux.sh.

install_linux.sh

@@ -40,10 +40,15 @@ install -m 0755 -o root -g root "${SCRIPT_DIR}/${BINARY_NAME}" "${INSTALL_DIR}/$
 rm -rf "${INSTALL_DIR}/templates"
 cp -a "${SCRIPT_DIR}/templates" "${INSTALL_DIR}/templates"
 chown -R root:root "${INSTALL_DIR}/templates"
+rm -rf "${INSTALL_DIR}/static"
+cp -a "${SCRIPT_DIR}/static" "${INSTALL_DIR}/static"
+chown -R root:root "${INSTALL_DIR}/static"
 chown "${SERVICE_USER}:${SERVICE_USER}" "${INSTALL_DIR}"
 chmod 0755 "${INSTALL_DIR}"
 find "${INSTALL_DIR}/templates" -type d -exec chmod 0755 {} \;
 find "${INSTALL_DIR}/templates" -type f -exec chmod 0644 {} \;
+find "${INSTALL_DIR}/static" -type d -exec chmod 0755 {} \;
+find "${INSTALL_DIR}/static" -type f -exec chmod 0644 {} \;
 
 SOCKET_PATH="${SOCKET_DIR}/web.sock"