dx: CONTRIBUTING.md references a testing command that doesn't match package.json scripts

[Xhristin3]

Problem Statement
CONTRIBUTING.md documents development workflow commands. Some may reference scripts that do not exist or have been renamed. First-time contributors following the guide encounter errors before they've made any changes.

Why It Matters
Broken contributor documentation is demoralising and signals poor project maintenance quality.

Acceptance Criteria

• Audit every command in CONTRIBUTING.md against the actual scripts in all package.json files
• Fix any discrepancies
• Add a CI step that validates npm run lint, npm run test, and npm run build all succeed
• Add a CONTRIBUTING.md badge linking to the contribution guide from the README

Files Affected: CONTRIBUTING.md, README.md

Difficulty: Easy | Effort: 1–2 hours

[grantfox-oss]

🦊 GrantFox — @Bug-Hunter-X has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #382)
2. Your PR will be reviewed by the XStreamRollz maintainers

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