Enable detekt rule: ComplexCondition

[AdrianLeeElder]

Summary

Re-enable the ComplexCondition detekt rule under complexity in backend/detekt.yml.

This rule is currently disabled (active: false) together with other rules that had widespread pre-existing violations. We want to turn rules back on incrementally.

Tasks

1. Set ComplexCondition.active to true under the complexity section in backend/detekt.yml (or remove the override if the default is already true).
2. From the backend/ directory, run ./gradlew detekt and fix reported violations. Use ./gradlew detektFormat where it helps for formatting-related fixes.
3. Keep CI green: the build uses maxIssues: 0.

Context

The comment at the top of backend/detekt.yml notes that disabled rules are candidates for incremental cleanup.