fix(skills): align guidance with Sent v3 contracts

[sent-dm]

Summary

• align template authoring and builder guidance with the current POST /v3/templates definition contract, variables, buttons, statuses, and webhook shapes
• refresh Sender Profile authentication and tenancy rules plus all three supported WABA integration paths
• replace stale 10DLC endpoint guidance with profile campaign APIs and separate API/evidence validators
• correct current RCS capabilities and distinguish automatic routing/fallback from explicit multi-channel broadcast
• make Claude commands thin wrappers around canonical skills
• add a checked-in v3 contract manifest, live drift check, and deterministic fixture, contract, and routing gates

Root cause

The skills mixed snapshot-era v2/v3 guidance with Meta Cloud API payloads. They also documented removed brand endpoints and treated multi-channel broadcasts as fallback behavior, which could cause duplicate sends and charges.

Impact

Users receive current Sent v3 payload, authentication, and routing guidance. Invalid examples are rejected in CI, generated adapters remain reproducible, and scheduled/release checks detect live OpenAPI or routing drift.

Validation

• python3 scripts/validate.py
• python3 scripts/test_contracts.py — 16 tests passed
• python3 scripts/test_validation_gates.py — 18 invalid mutations rejected
• python3 scripts/test_fixtures.py
• python3 scripts/check_live_contract.py
• all 13 skills passed skill-creator quick validation
• plugin and Claude manifests validated
• python3 scripts/generate_adapters.py --check
• git diff --check