feat(integrations): add HttpClawHubClient for CG-010

[ysqander]

Motivation

• Implement the ClawHub integration required by ticket CG-010 so scans can be enriched with marketplace metadata and remote SKILL.md retrieval.
• Ensure provider verdicts are normalized to the shared ThreatIntelVerdict contract and degrade to a neutral unknown verdict when fields are missing.

Description

• Add HttpClawHubClient in packages/integrations/src/clawhub-client.ts with getSkill, getSkillMarkdown, and listSkills implementations against the ClawHub endpoints.
• Introduce IntegrationHttpError in packages/integrations/src/errors.ts and re-export the new surface via packages/integrations/src/index.ts.
• Add unit tests in packages/integrations/src/clawhub-client.test.ts covering neutral degradation, explicit provider verdict parsing, markdown retrieval, and listing behavior, and add a test script to packages/integrations/package.json.
• Normalize provider verdict fields into ThreatIntelVerdict while safely handling optional numeric and string fields to satisfy exactOptionalPropertyTypes.

Testing

• Ran pnpm build and the workspace build completed successfully including the new integrations code.
• Ran pnpm typecheck and full workspace typecheck passed.
• Ran pnpm test where @clawguard/integrations tests passed but the overall workspace run failed due to an existing failing test in @clawguard/discovery that is unrelated to this change.

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Codex Task