fix(curogram-mcp): address PR #67 second-round review blockers

- curogram send: add a fail-closed conversation/patient linkage check
  (verifyConversationPatientLink) before POSTing. Refuses to send unless
  the consent-checked patient_id is a participant in conversation_id, so a
  mismatched id can never leak PHI into the wrong patient's thread.
- ringcentral read_device_sip_info: redact SIP secrets (password,
  authorizationId, userName, domain, outboundProxy) by default. Raw
  credentials are returned only with reveal_secrets=true AND the exact
  per-device approval_text from the redacted response.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>