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

[kpal81xd]

Part of the v3 rollout — playcanvas/eslint-config#48 (Wave 2).

What changed

• Subpath migration: replaced the v2 default-import spread with the /typescript subpath export.
• Pinned @playcanvas/eslint-config to 3.0.0-beta.6.
• Removed hand-wired @typescript-eslint parser/plugin, the tsPlugin.configs.recommended rules spread, and the import/resolver settings block — all now provided by the shared /typescript config. Dropped the now-unused @typescript-eslint/eslint-plugin, @typescript-eslint/parser, and eslint-import-resolver-typescript devDeps. Renamed preserved rule overrides from the import/* to the import-x/* namespace; kept repo-specific ignores, per-file globals, and rule disables.

Lint status

Draft — 33 errors / 2 warnings remain. Strict-mode triage tracked in playcanvas/eslint-config#48; not fixed here per the rollout policy.