fix: improve gift code flow

[ovitrif]

Fixes #680

Improves the UX of the Easter Egg gift code redemption flow by adding better logging, error handling, and validation.

Description

• Add comprehensive logging throughout gift claim operations for better debugging
• Fix amount=0 handling to allow backend validation instead of rejecting upfront
• Improve error messages with full error chain context
• Add operation guards to prevent duplicate claim attempts
• Validate that channel funding transaction exists
• Better error classification (Used/UsedUp/Error)

QA Notes

Test scenarios:

1. Test with a valid gift code (happy path)
2. Test with a gift code that has amount=0 in QR
3. Test with an already-used gift code
4. Test with an exhausted/depleted gift code
5. Test in both liquidity scenarios (with/without existing channels)
6. Monitor logs to verify detailed debug information is captured

Warning

⚠️ Code was not compiled or tested due to build permission constraints. Please run:

• ./gradlew compileDevDebugKotlin to verify compilation
• ./gradlew testDevDebugUnitTest to run tests
• ./gradlew detekt to check for lint issues