chore: add oxlint, oxfmt and golangci-lint

[kellylimmm]

Closes #2

Summary

• Adds oxlint@1.69.0 and oxfmt@0.54.0 as pinned devDependencies with lint and format scripts at the repo root
• Adds golangci-lint v2.12.2 installed into bin/ via Makefile (make install-tools, make lint)
• Commits config files: .oxlintrc.json, .oxfmtrc.json, .golangci.yaml
• Adds .vscode/extensions.json and .vscode/settings.json recommending oxc.oxc-vscode + golang.go and setting oxc as the default formatter for JS/TS/config files

Test plan

• pnpm install completes without errors
• pnpm format exits zero on a correctly formatted workspace
• pnpm lint exits zero when JS/TS source files have no violations
• make install-tools downloads golangci-lint v2.12.2 into bin/
• make lint passes on a clean Go module
• Opening the repo in VS Code prompts to install oxc.oxc-vscode and golang.go
• oxfmt is not the default formatter for .go files

🤖 Generated with Claude Code

The base branch was changed.