chore: adopt oxlint as lint gate

[ElbertePlinio]

No linter today (only typecheck + vitest). Node-only TS monorepo, 7 packages. Effort: S.

Agent plan

Goal: oxlint is the primary lint gate (edit loop + CI), per workspace AGENTS.md "Frontend tooling". Audit source: oxlint 1.80.0 run on this tree, 2026-08-25.

Checklist:

• Add oxlint + .oxlintrc.json at root
• Fix 12 baseline findings (9 no-useless-escape, 2 no-control-regex, 1 unicorn) or disable no-control-regex with justification
• Add CI Lint step
• lint script runs oxlint; CI "Lint" step uses it
• Baseline is clean (fix findings or justify per-rule disables in .oxlintrc.json)
• PR/review

Validation:

• bunx oxlint (or npx oxlint) exits 0 on the tree
• CI green

Current status: Planned
Next action: open PR