Migrate to @playcanvas/eslint-config v3 (/javascript)

[kpal81xd]

Part of the v3 rollout — playcanvas/eslint-config#48 (Wave 5 — highest blast radius).

What changed

• Subpath migration: switched the root config to the /javascript (= /legacy) subpath export.
• esmScriptTags: replaced the v2 playcanvasConfig.find(...) definedTags hack with the direct import { esmScriptTags } from '@playcanvas/eslint-config'. The old hack located the config entry carrying jsdoc/check-tag-names, read its definedTags, and re-set the rule to [...new Set([...existingTags, 'range', 'step', 'precision'])]. In v3 esmScriptTags already includes range/step/precision, so the rule override now sets definedTags: [...new Set([...esmScriptTags, 'alpha', 'beta', 'category', 'import'])] — preserving the shared config's own extra tags that the override would otherwise drop.
• examples/ config: migrated to /javascript + /react. The hand-rolled minimal jsxUsesVars rule was removed since eslint-plugin-react (bundled by /react) provides react/jsx-uses-vars natively; all repo-specific bits (custom examples/* config-block rules, importOrder, globals, max-len, ignores) are preserved. The config loads and parses cleanly, but /react's recommended ruleset surfaces a large new error volume that still needs tuning — see Lint status. Rule triage for examples/ is still TODO.
• Pinned @playcanvas/eslint-config to 3.0.0-beta.6 in both the root and examples/ packages.

Lint status

Draft — both configs load cleanly (no config-invalid / import / parse crashes).

• Root (npm run lint): 6 errors / 3 warnings. Drop-in vs v2; remaining items are pre-existing JSDoc/import strict-mode nits (jsdoc/require-hyphen-before-param-description, one inline @type, import/no-named-as-default).
• examples/ (npm run lint): 1830 errors / 0 warnings, dominated by rules newly introduced by /react: react/react-in-jsx-scope (1379 — obsolete under the React 19 JSX transform these examples use), react/prop-types (232), and the stricter legacy import/extensions (219). These need deliberate config tuning (disable react-in-jsx-scope / wire up the jsx-runtime, decide on prop-types, relax import/extensions), not source fixes.

Strict-mode/JSDoc triage tracked in playcanvas/eslint-config#48; not fixed here per the rollout policy.