Fix Stamped.io connector merge blockers

[andrei-hasna]

Summary

• adds the Stamped.io connector from PR feat(marketing-sales): add Stamped.io reviews & loyalty connector #288 with private auth corrected to the documented stamped-api-key header
• moves customer creation and loyalty point adjustment to the documented v3 endpoints, with README references to Stamped official docs
• fixes connector package build/pack output, hardens private profile file mode to 0600, and updates tests for the corrected contract
• adds a small connectors CLI webhooks list --json compatibility shim for the existing root CLI test contract with @hasna/events 0.1.13

Official Stamped references

• https://developers.stamped.io/docs/getting-started.md
• https://developers.stamped.io/reference/createcustomer.md
• https://developers.stamped.io/reference/adjust-points.md

Validation

• cd connectors/stampedio && bun run typecheck
• cd connectors/stampedio && bun test (13 pass, 0 fail)
• cd connectors/stampedio && bun run build && test -f dist/index.js && test -f dist/index.d.ts && bun pm pack --dry-run
• bun run typecheck
• bun run build
• HOME="$(mktemp -d /tmp/open-connectors-home.XXXXXX)" bun test (1200 pass, 0 fail)
• git diff --cached --check
• staged secret scan: no real credential matches after placeholder exclusion

Addresses merge blockers reported on #288.

GitHub author is andrei-hasna
GitHub reviewer pool: andrei-hasna, kriptoburak
Selected non-author reviewer: kriptoburak