Add test coverage for core financial packages

[dotunv]

Description

Fluxa has only 6 test files out of 85 Go source files (7% coverage). Most critically, core financial logic has zero tests.

Untested Packages (Priority Order)

Critical (Financial)

1. settlement/ - Builds, signs, and submits Stellar transactions
2. transfer/ - Transfer initiation, fee calculation, queue dispatch
3. fx/ - FX quotes, conversion execution, DEX path payments
4. reconcile/ - DB vs Horizon verification, stuck tx recovery
5. wallet/ - Wallet CRUD, balance retrieval

High Priority

6. fiat/ - Fiat on/off-ramp, Flutterwave integration
7. alerting/ - Webhook-based alerting
8. tenant/ - Multi-tenant context scoping
9. apikey/ - Key generation, hashing, verification
10. config/ - Environment config with validation

Medium Priority

11. postgres/ - Repository implementations
12. queue/ - Asynq task definitions
13. server/ - Middleware (request ID, logging, auth)

Testing Stack

• Go standard testing package
• Testify for assertions
• sqlmock for database mocking
• Redis mock for cache testing

Acceptance Criteria

• Each critical financial package has unit tests
• Each critical financial package has integration tests
• `go test ./..." passes
• Test coverage >50% for financial packages

Labels

testing backend help wanted

[Babigdk]

I'm interested in working on this issue.

I have experience writing and expanding Go test suites for backend services, including financial workflows, database interactions, and API logic. I'll prioritize the critical financial packages, add both unit and integration tests using testing, testify, sqlmock, and appropriate mocks, while keeping the suite reliable and maintainable. I'll ensure go test ./... passes and work toward the requested coverage targets without introducing regressions. I'd appreciate being assigned this issue.