feat(twilio): add SMS integration MVP and dev-only settings gating

[DJJones66]

Summary

This PR adds the BrainDrive Twilio SMS MVP and related local/dev integration work so SMS can be tested as a Gateway client without exposing the feature broadly yet.

What’s included

• Add Twilio SMS settings, webhook handling, test-send flow, and Gateway integration.
• Add dev-only visibility for the SMS (Twilio) settings tab.
• Keep the Twilio webhook publicly reachable through the Gateway auth/pre-handler path.
• Add /twilio proxy support in the Vite dev server for local/dev testing.
• Update dev compose config so dev installs report install_mode=dev.
• Add named-tunnel-friendly allowed host support for dev web access.

Why

This keeps SMS testing available for developers and testers while avoiding exposure in local, quickstart, and production installs until the workflow is more fully validated.

Testing

• Verified targeted Twilio/settings tests pass.
• Verified config tests pass.
• Verified client typecheck passes.
• Verified TypeScript build passes.
• Verified dev stack now reports install_mode=dev via /api/config.

Notes for testers

• SMS (Twilio) appears only when running a dev install.
• Dev stack should be started with the dev compose flow so BRAINDRIVE_INSTALL_MODE=dev is present.
• Twilio webhook and named tunnel testing should use the generated BrainDrive webhook URL exactly.

Risks / Follow-up

• Twilio and tunnel setup are environment-sensitive, so end-to-end testing still depends on correct external configuration.
• The feature is intentionally gated to dev installs for now.
• Additional polish or broader rollout controls may still be needed before merging to production-facing flows.