refactor: consolidate shared types and add oxfmt formatting

[makinosp]

Summary

Two changes bundled on this branch (as agreed):

1. Refactor commits — consolidate shared GitHub review DTOs and inline-finding types into src/types.ts and tighten encapsulation (export → module-private) in src/domain/post-comments.ts.
2. Formatting — add oxfmt as a dev dependency and format the codebase with it.

What's included

Refactor (existing commits)

• refactor: consolidate shared types in types.ts and tighten encapsulation (9aa0f9c)
• refactor: centralize GitHub review DTOs and inline-finding type in types.ts (5105be2)

Formatting (03809de)

• Add oxfmt ^0.62.0 to devDependencies (package.json, pnpm-lock.yaml)
• Add oxfmt.config.ts matching the existing codebase style:
  • singleQuote: true
  • printWidth: 120
  • sortImports: false
  • ignorePatterns: ['.vendor/**'] (protects the vendored submodule)
• Format the codebase with oxfmt; normalize all files to LF line endings
• Document the dev commands (pnpm typecheck / lint / format / test) in the README

Verification

• pnpm typecheck ✅
• pnpm test — 191/191 pass ✅
• pnpm lint ✅
• oxfmt --check ✅

Note: duplicate-review-prevention changes are intentionally not in this PR — they live in a separate branch based on main.