Fix rendering issues: mermaid, table width, display math, cpp highlight

[patakuti]

Reported Issues

1. Mermaid diagrams not rendering

   • When a theme is saved in localStorage, the theme restore script calls mermaid.initialize({startOnLoad: false}), overriding the initial config before DOMContentLoaded fires, so diagrams are never rendered.

2. Table column widths are equal

   • width: 100% causes columns to be distributed equally.
   • Column widths should adjust to content.

3. Display math ($$...$$) is too large

   • Block math renders too large relative to body text.

4. No syntax highlighting for ```cpp

   • C++ code blocks appear uncolored (or colors are too subtle to notice).

Resolution

• Implement markdown-proxy server #1: Switch to startOnLoad: false + explicit mermaid.run() in DOMContentLoaded; pin CDN to mermaid@10
• Add SSRF protection, HTTP timeout, and access logging #2: Change to width: auto; table-layout: auto
• Add live reload for local files using SSE + fsnotify #3: Add .math.display { font-size: 0.9em; overflow-x: auto }
• Add math rendering support using goldmark-mathjax and KaTeX #4: Investigation shows highlighting is working correctly; the github Chroma style uses near-black for control-flow keywords which may look unstyled — recommend hard refresh to clear CSS cache

Related PR

#57