OPS-6978 Fix OpsLevel checks

[whodeen]

Summary

• Upgrade ESLint to v10 and @shelf/eslint-config to the matching v6 config.
• Migrate formatting from Prettier to Oxfmt with repo-local config and lint/lint-staged wiring.

Validation

• COREPACK_HOME=/tmp/corepack npm_config_cache=/tmp/npm-cache COREPACK_ENABLE_DOWNLOAD_PROMPT=0 corepack pnpm@10.25.0 install --frozen-lockfile --config.strict-dep-builds=false
• COREPACK_HOME=/tmp/corepack npm_config_cache=/tmp/npm-cache COREPACK_ENABLE_DOWNLOAD_PROMPT=0 corepack pnpm@10.25.0 lint:ci
• COREPACK_HOME=/tmp/corepack npm_config_cache=/tmp/npm-cache COREPACK_ENABLE_DOWNLOAD_PROMPT=0 corepack pnpm@10.25.0 type-check
• COREPACK_HOME=/tmp/corepack npm_config_cache=/tmp/npm-cache COREPACK_ENABLE_DOWNLOAD_PROMPT=0 corepack pnpm@10.25.0 test
• COREPACK_HOME=/tmp/corepack npm_config_cache=/tmp/npm-cache COREPACK_ENABLE_DOWNLOAD_PROMPT=0 corepack pnpm@10.25.0 build

Notes:

• Local pnpm has strict-dep-builds=true globally, so install validation disabled that local-only guard; install still reported ignored build-script warnings for existing native packages.
• ESLint 10 peer warnings remain from upstream plugins, but lint/type-check/test/build pass.