P4-4: Update existing gateway implementations

[tcheeric]

Description:
Implement new Gateway methods in phoenixd and dummy gateways.

Changes required:

• Implement getPaymentType() and getGatewayId() in each gateway.
• Update any callers expecting new methods.

Acceptance criteria:

• All gateway implementations compile with new interface methods.
• Runtime wiring still resolves gateways correctly.

Estimated hours: TBD
Priority: Medium
Branch name: refactor/phase-4-task-4
Dependencies: P4-3