build: migrate from pnpm to bun as package manager

[vanceingalls]

Summary

• Replace pnpm with bun for dependency installation, script running, and ad-hoc execution
• Keep pnpm for publish workflow only (publishConfig overrides + --provenance)
• bun install replaces pnpm install (~4-5x faster cold installs)
• bun run replaces pnpm run (~28x less startup overhead)
• bunx replaces npx in lefthook hooks
• CI workflows updated (oven-sh/setup-bun@v2 + actions/setup-node@v4)
• pnpm-lock.yaml removed, bun.lock generated
• pnpm-workspace.yaml kept for publish compatibility
• CLI source code (packages/cli/src/) unchanged — shipped to end users who may not have bun

Part 5/5 of VA-851

Test plan

• bun run lint — 0 errors
• bun run format:check — all files pass
• bun run build — all 5 packages build
• 330 core tests pass
• 18 engine tests pass
• publish.yml unchanged (pnpm stays for npm publishing)
• No bunx/bun run references in shipped source code (packages/*/src/)

[linear]

VA-851 [Pre-Migration] Configure ESLint, Prettier, and conventional commits

Context

The codebase currently has no linting or formatting enforcement. Code is clean by convention, but OSS contributors need automated guardrails. Team feedback: "I love when an open source repo has this."

What to do

1. ESLint — add configuration at monorepo root with TypeScript rules. Extend from @typescript-eslint/recommended.
2. Prettier — add .prettierrc at root. Configure for the existing code style (double quotes, no semicolons or with — match what's already there).
3. Conventional commits — add commitlint config enforcing conventional commit format (feat:, fix:, refactor:, etc.). This enables automated changelog generation later.
4. Run formatter across all source files to establish baseline (single "format" commit in internal repo before port).
5. Add lint/format scripts to root package.json: pnpm lint, pnpm format, pnpm format:check
6. Verify all existing code passes lint + format checks with zero errors

Why before port

We want the OSS repo's first commit to already have these configs in place and all code conforming. No "fix linting" commits in public history.

[vanceingalls]

• perf: replace tsc with tsgo for ~3x faster type checking #29
• build: migrate from pnpm to bun as package manager #28 👈 (View in Graphite)
• ci: add lint and format check job, update CONTRIBUTING.md #26
• style: apply oxfmt baseline formatting across all source files #25
• fix: resolve oxlint errors across codebase #24
• build: add oxlint, oxfmt, commitlint, lefthook, knip, and editorconfig configs #23
• main

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