feat!: add no-reduce-accumulator-copy rule

[davidding]

Purpose / Goal

Adds an ESLint rule that flags O(n²) accumulator copies inside reduce/reduceRight callbacks — object spreads ({ ...acc }, [...acc]), and acc.concat() — and directs developers toward a for...of loop with mutation or a purpose-built method (e.g. flatMap, Object.groupBy).

Summary of Changes 📋

• Add plugins/hs-web-team/rules/no-reduce-accumulator-copy.js — ESM named export, implemented using context.sourceCode.getScope(node) (ESLint v9 flat config API)
• Add plugins/hs-web-team/index.js — shared plugin registry; exposes hsWebTeamPlugin.configs.recommended (following the typescript-eslint/eslint-plugin-react pattern) so both index.js and browser.js spread a single config object rather than duplicating plugin registration. Rules are co-located under plugins/hs-web-team/rules/ following the same layout as standalone ESLint plugin packages.
• Add eslint.config.js — repo-local config that extends the shared Node config; adds Cypress globals for cypress/** so no-undef does not false-positive on Cypress/cy
• Remove eslint.config.js from commonIgnores in both configs — config files should meet the same lint standards as any other file
• Update lint script to eslint . (was eslint -c ./index.js *.js) so all subdirectories are covered without an explicit include list
• Add tests/plugins/hs-web-team/no-reduce-accumulator-copy.test.js — 10 test cases via node:test + ESLint RuleTester, covering object spread, array spread, concat, reduceRight, in-place mutation (valid), and non-accumulator spreads (valid)
• Set npm test to node --test and add a test step to the PR workflow
• Add files field to package.json — scopes the published tarball to only the files consumers need; excludes tests, .github/, .githooks/, eslint.config.js, and CLAUDE.md
• Add examples/custom-rules.md — documents the bundled hs-web-team plugin rules with bad/good code examples and remediation guidance
• Update README.md — add "Custom Rules" section and index entry linking to the new examples file

Screenshot(s) or GIF(s) 📸

N/A - No UI changes

Production Checklist ✅

• No additional steps required

Relevant Links 🔗

• N/A

Coding Standards Doc ⌨️

• Coding Standards

[darkmavis1980]

Also don't forget to set the version properly to be a minor

[davidding]

Also don't forget to set the version properly to be a minor

@darkmavis1980 Version numbers are automatically handled by the release workflow, based on conventional commit messages - #52

[denisolvr]

question: Is the -copy.js files on purpose named as copy?

[davidding]

question: Is the -copy.js files on purpose named as copy?

@denisolvr - Yes, the new rule is no-reduce-accumulator-copy.