refactor(eslint-plugin): concise-method shorthand for rule visitor objects (reconstruct #542 on master)

[kriscendobot]

Provenance (why this PR exists)

Reconstructs #542, which was errantly merged to master --
a master-based (upstream-destined) change should have been closed once its upstream
endojs/endo equivalent merged (or closed explicitly), not merged into the fork's
master. Fork master periodically hard-re-mirrors from upstream and silently drops
fork merge-commits, so this change is on borrowed time and invisible upstream. Reopened
here (as a fresh PR, since GitHub cannot reopen a merged PR) to surface it for maintainer
attention -- to ferry upstream to endojs/endo or close.

• Original PR: refactor(eslint-plugin): concise-method shorthand for rule visitor objects #542
• Original merge commit: 1bb6e7fc22 (merged f87f2cc928 into master)
• This branch cherry-picks f87f2cc928 onto a frozen snapshot of master taken at
  87823d83d1 (the original merge's first parent -- the state after refactor: retire function-keyword in favor of arrow/method syntax per erights review #474, before refactor(eslint-plugin): concise-method shorthand for rule visitor objects #542),
  so the diff shown here is exactly the original change. The reconstructed diff was
  verified byte-identical to git diff 87823d83d1 f87f2cc928.

Relationship to #474 (bundle the ferry if desired)

This is a follow-up to #474 (retire-function-keyword), whose
upstream form is endojs/endo#3312 / endojs/endo#3318. No upstream endojs/endo PR
exists for this shorthand follow-up yet. If the maintainer ferries #474's upstream
equivalent, this change (concise-method shorthand for the rule-file visitor objects) is
a natural companion to bundle alongside it.

---

What this does (original #542 description)

Follow-up to #474. On #474, @kriscendobot offered to convert the
@endo/eslint-plugin rule visitor objects to concise-method shorthand, and @erights
asked for it in a follow-up PR ("Please do so in a follow-up PR"). This is that follow-up.

Why #474 could not do it

The object-shorthand rule runs with avoidQuotes: true (inherited from
eslint-config-airbnb-base via @endo/style). Quoted AST-selector visitor keys
('Program:exit'(node) { ... }) are exactly the case avoidQuotes exempts, so those
handlers were left as non-shorthand properties in #474.

The change

1. Scoped relaxation. Adds an overrides entry to
   packages/eslint-plugin/package.json's eslintConfig, scoped to lib/rules/*.js,
   setting object-shorthand: ['error', 'always', { avoidQuotes: false }]. This is a
   targeted relaxation for the rule-file visitor-object idiom, not a global flip.
2. Applies the shorthand to the now-eligible handler. Running eslint . in the
   package after the relaxation flags exactly one handler: the anonymous
   'Program:exit': function () { ... } in lib/rules/harden-exports.js. It becomes
   'Program:exit'() { ... }, and the func-names disable directive the conversion
   orphaned is removed.

The assert-fail-as-throw.js 'Program:exit' / Program handlers are named
function expressions (restoreAssertFailAsThrow, installAssertFailAsThrow), which
object-shorthand never converts (shorthand would drop the name), so they are correctly
left untouched.

Pure-shorthand conversion: no behavioral change.

---

Draft: reconstruction surfaced for maintainer triage (ferry upstream or close). Base is
the frozen snapshot master-87823d8.

[kriscendobot]

Shepherd update

Head SHA: 142dd0e760c72374b77479d5c59647543d8625d1

• 142dd0e760 (chore(ci): refresh setup-node v6 pin) updates the pinned actions/setup-node v6 commit across the workflows, resolving the persistent zizmor version-comment findings.
• The initial matrix-wide setup-node failures were transient GitHub action-manifest resolution failures; a rerun passed once service resolution recovered. No product-code change was needed.

Verification: all checks are green on the head SHA, including CI, Workflow security audit, and mutual-dependency build. CI: https://github.com/endojs/endo-but-for-bots/actions/runs/29543258286