Move Agent HTML Render to Node 24 LTS

[RiadMefti]

What changed

• Raise the runtime floor from Node 20.19 to Node 24.15 LTS.
• Test the supported floor on Node 24.15 and the newest runtime on Node 26.
• Update jsdom from 29.1.1 to 30.0.1.
• Stage the compatibility change as Agent HTML Render 0.4.0.

Compatibility

Node 20 and Node 22 are no longer supported. The runtime engine is ^24.15.0 || >=26.0.0.

Verification

• Node 24.15: type checking and 26 unit tests
• Node 26: type checking and 26 unit tests
• Production Chromium review test
• Strict Codex, Claude Code, and OpenCode smoke check
• npm package dry-run
• npm audit: 0 vulnerabilities