feature: spark address as username

[r1n04h]

Note

Enables using a Spark address directly in the LNURL-pay callback by validating with isSparkAddress and falling back to DB lookup; adds tests for the validator.

• API
  • Update GET /api/lightning-address/:username/callback to accept either a Spark address or username.
    • Validate amount and username.
    • Use isSparkAddress(username) to decide between direct use or DB lookup via databaseService.getSparkAddressByUsername.
    • Generate invoice with createInvoiceForSparkAddress.
• Spark Service
  • Add isSparkAddress(address) to validate Spark bech32m addresses.
• Tests
  • Add test/spark-service.test.ts covering isSparkAddress true/false cases.

^{Written by Cursor Bugbot for commit d8b8e39. This will update automatically on new commits. Configure here.}