test: add social source validation fixture

[kriptoburak]

Summary

• Add a realistic social-source-review skill regression with license, compatibility, metadata, allowed-tools, enforced references, and reference validation enabled.
• Keep the skill read-only: TweetClaw is source evidence only, while drafting, scoring, scheduling, posting, and approval stay outside the fixture.
• Apply the formatter-required export ordering so the target lint gate passes.

Validation

• pnpm install --frozen-lockfile
• pnpm type-check
• pnpm check
• pnpm test
• pnpm build
• git diff --check
• changed-diff public hygiene scan