docs(ringcentral-admin): document all write tools + SIP reveal gating

README listed only create_ai_scheduling_extension as a write tool. Enumerate
the queue/routing write tools, document the EXULT_RC_ALLOW_SECRET_READS gate
for raw SIP reveal, and note the pending scope decision (PR #67).

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