Release 0.21.1

[zackbart]

Summary

• bump the package, runtime constant, generated Node pin, upgrade guide, and changelog to 0.21.1
• publish the Cloudflare and Notion contract fixes merged in Reconcile provider contracts and Cloudflare outputs #511
• reconcile current Linear, Stripe, Mixpanel, and RevenueCat hosted catalogs
• retain plan-scoped catalog supersets where one authenticated workspace cannot prove global removal

Drift review

The local shell had no maintainer hosted-provider variables, so the authenticated BePresent deployment supplied exact live catalog names, annotations, and Mixpanel schemas. The recheck found:

• Stripe: 11 observed, 11 reviewed, no additions, removals, conflicts, or schema findings
• Mixpanel: 64 observed, 64 reviewed, no additions, removals, conflicts, or schema findings
• Linear: no unreviewed additions or conflicts; five customer-request names remain in the documented plan-aware superset
• RevenueCat: no unreviewed additions or conflicts after preserving the deliberate screenshot exception; credential-scoped absences remain in the documented superset
• Cloudflare and Notion: no drift across 49 and 14 touched endpoints

Verification

• npm run release:check
• npm run drift:check -- --specs
• authenticated BePresent catalog and schema comparison
• 2,740 tests passed, 40 skipped
• production dependency audit clean
• packed generated-container smoke passed

Closes #512