feat: add Twilio integration

[pranavrajs]

Adds the Twilio integration (Others). Check SMS, MMS, and WhatsApp message delivery, call history, and phone number validity in Twilio.

Tools

• Find Messages to Number (find_messages_to_number, GET)
• Find Messages from Number (find_messages_from_number, GET)
• Get Message (get_message, GET)
• Find Calls to Number (find_calls_to_number, GET)
• Find Calls from Number (find_calls_from_number, GET)
• Look Up Phone Number (lookup_phone_number, GET)

Testing

• The manifest passes the validator ("valid": true).
• Every template was rendered locally with Liquid 5.4.0 against sample responses built from Twilio's API docs.
• Not run against the live API. No credentials were available, so tool-tester.rb has not been run with a real key. This needs doing before merge.
• No logo is included.

Review notes

• Outbound message text is deliberately left out so Captain cannot leak one-time codes.
• No write tools: Twilio writes are form-encoded and Captain only sends JSON.

The root README.md row and .env.example entry for this integration are in a separate PR, so the per-integration PRs do not conflict with each other.

[pranavrajs]

Closing: developer tools are out of scope for this catalog.