feat(plg): add spacecatOrgId support to PLG onboarding controller[WIP]

[Kanishkavijay39]

• resolveImsOrgId helper resolves imsOrgId from a Spacecat Organization UUID
• onboard endpoint accepts spacecatOrgId in body (skips token-tenant validation)
• getStatus endpoint accepts spacecatOrgId via new route GET /plg/onboard/status/org/:spacecatOrgId
• 97 unit tests, 100% statement/branch/line coverage

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This PR will trigger a minor release when merged.