fix: MathJax-related fixes

[QEDK]

• removes custom window handling for mathjax
• bumps mathjax lib to latest stable
• bumps bundler and deps to latest stable
• fix inline mathjax missed earlier
• adds a MathJax section to README

[Copilot]

Copilot review overview

🔵 Needs a closer look

The feature's correctness depends on a third-party CDN SRI integrity hash and many gem sha256 checksums that cannot be verified in this offline environment and warrant a human confirming the site still builds and renders math.

Review effort: Balanced
Findings: None

What changed in this PR

This PR modernizes the MathJax setup for the Jekyll-based Monad Improvement Proposals static site. It removes the custom client-side window.MathJax single-$ configuration in favor of relying on Kramdown's server-side math conversion (which emits \(...\)/\[...\]) plus MathJax 4's default delimiters, fixes a stale inline-math expression in MIP-10, documents the math conventions in the README, and bumps the bundler/gem dependencies.

Changes:

• Switch MathJax loading to detect Kramdown-rendered \[/\( and load MathJax 4.1.3 (dropping the custom $-based config and the page.mip guard so math works on any page).
• Fix MIP-10 inline math: convert $...|V|...$ to $$...\lvert V \rvert...$$ so Kramdown renders it and the vertical bars aren't parsed as a table.
• Document math usage in the README and bump Gemfile.lock dependencies (MathJax-adjacent build deps, bundler 4.0.22).

File	Description
_layouts/​default.html	Replaces custom MathJax config/detection with a simpler \[/\( check and MathJax 4.1.3 script.
MIPs/​MIP-10.md	Converts the one remaining single-$ inline expression to $$...$$ with \lvert/\rvert.
README.md	Adds a "Math" section documenting Kramdown $$ delimiters and the \lvert/\rvert convention.
Gemfile.lock	Bumps gems (google-protobuf, sass-embedded, listen, bigdecimal, jekyll-feed, jekyll-seo-tag) and bundler to 4.0.22.

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