CI improvements - 2023/07

[chalin]

Misc. CI improvements:

• [CI] fix:refcache - ensure all packages are installed #3072
• CI: make netlify-cli optional #3084
• Spelling:
  • [CI] Add action to check page-local dictionaries, and more #3095
  • Normalize cSpell front-matter dictionnaires #3093
  • [CI] fix:dict - ensure workflow fails if files have changed #3116
  • CI: run spelling checker #948
• [CI] Adjust spell-check action's path to omit registry entries #3097
  • [CI] package.json: fix test script #3099 -- oops, made that last edit too quickly!
• [CI] remove global dict words from page-local dictionaries + handle more cases #3101
• [CI] Clone submodules more deeply for /fix:refache #3103 && [CI] Clone submodules more deeply for /fix:refache -- take 2 #3110
• Site build info:
  • [CI] Publish site-build info under /site #3111
  • [CI] Add timezone to build timestamp #3113
• [CI] Markdown lint: drop unnecessary config; add lang to code-fences #3115
• CI: check file formatting, including markdown #1063
  • CI: run markdown linter on all pages + fixes #3032
  • CI: lint-md task tweaks #3036

Carried over to #3122:

• Make npm-run-all optional or replace it with a simple script or task, since we only use it to run scripts sequentially