docs: Add check:source script to CONTRIBUTING.md (#14)

Co-authored-by: Claude Sonnet 4.5 <[email protected]>

Author: roottool

CONTRIBUTING.md

@@ -86,6 +86,7 @@ Before implementing:
 Run these commands before submitting:
 
 ```bash
+bun run check:source # Linting and formatting must pass
 bun run check:type   # TypeScript type checking must pass
 bun run test         # All tests must pass
 bun run build        # Build must succeed
@@ -121,6 +122,7 @@ Before submitting a PR:
 - [ ] Read AGENTS.md implementation rules
 - [ ] Confirmed change does not violate the boundary
 - [ ] Added tests for new functionality
+- [ ] Linting and formatting passes (`bun run check:source`)
 - [ ] All tests pass (`bun run test`)
 - [ ] Type checking passes (`bun run check:type`)
 - [ ] Build succeeds (`bun run build`)