Add middleware tests

[osvaldoandrade]

Test all middleware components.

Current coverage:

• Only auth_test.go (120 LOC)

Missing tests:

• rate_limit_test.go
• logger_test.go
• tracing_test.go
• tenant_test.go
• request_id_test.go
• worker_auth_test.go
• any_auth_test.go
• worker_scope_test.go

Implementation:

• Add unit test per middleware
• Table-driven where applicable
• Test middleware chain composition

Acceptance criteria:

• All middleware tested
• Coverage ≥90% on middleware package

Part of: #654
Requires: #649 (middleware consolidated)