fix(auth): reuse parsed debug sms body

[aiirvizionz]

Summary

• parse the debug SMS POST body once and reuse it for test-verify requests
• prevent valid test-verify diagnostics from failing when the request body is read a second time
• return a 400 response for malformed debug SMS JSON payloads

Validation

• git diff --check
• node node_modules\vitest\vitest.mjs run --config $env:TEMP\qryptchat-vitest-minimal.config.mjs "src/app/api/auth/debug-sms/route.test.js" (4 tests)

Billing

• uGig billable PR candidate: expected invoice $0.50 if accepted/merged
• Not counted as revenue until paid/settled