ESLint config gap: no-undef + plugin-resolution errors on shell.js, app.mjs, functions, config

[mriechers]

Description

ESLint reports ~37 no-undef errors (plus a no-unsanitized/property plugin-resolution error) because eslint.config.js only grants browser globals to formatter/app.js and og-image/app.js — it never lists the files that have since been added.

Context

• Discovered during session on 2026-06-24 (formatter stray-break feature work)
• eslint.config.js browser-globals block targets only formatter/app.js, og-image/app.js. Files NOT covered, producing no-undef on customElements/document/window/fetch:
  • shared/shell.js
  • formatter/app.mjs
  • og-image/functions/* (worker globals)
  • eslint.config.js itself (Node require/module.exports under the generic **/*.js script block with no node globals)
• Also a no-unsanitized/property plugin-resolution error on the innerHTML lines in formatter/app.mjs (~1089/1200).
• Pre-existing; not introduced by the stray-break feature. No CI runs eslint today, so this doesn't block deploys — but npx eslint . is currently red.

Suggested fix

• Extend the browser-globals files glob to include shared/**/*.js and formatter/**/*.mjs (or switch to a broader browser glob with targeted Node/worker overrides).
• Add a Node-globals block for eslint.config.js / root config files.
• Resolve or remove the no-unsanitized plugin config so it loads cleanly.
• Optionally wire npx eslint . into CI once green.

Notes

• Created by /wrap-up during session review.
• Flagged explicitly to the user during the session as "worth a separate cleanup PR."