Add unit tests for gate-evaluator module

[nikolasdehor]

Problem

The gate-evaluator.js module (494 lines) in .aios-core/core/orchestration/ has zero test coverage. This module evaluates quality gates between epics to prevent bad outputs from propagating through the pipeline.

Solution

Add comprehensive unit tests covering:

• GateVerdict enum and DEFAULT_GATE_CONFIG exports
• Config loading — custom config, YAML file loading with merge, fallback to defaults, error handling
• Epic 3 checks — spec_exists (specPath, artifacts), complexity_assessed, requirements_defined
• Epic 4 checks — plan_complete (planPath, flag), implementation_exists (path, codeChanges), no_critical_errors
• Epic 6 checks — qa_report_exists, verdict_generated, tests_pass
• Additional checks — minScore conditional, requireTests with array/object/skipped formats, minTestCoverage threshold
• Verdict determination — strict mode (AC7), critical/high severity handling, blocking vs non-blocking gates, allowMinorIssues
• Score calculation — perfect, partial, zero, empty-checks scenarios
• Results storage (AC6) — getResults, getResult, getSummary, clear
• Logging — evaluation step logging, copy semantics

Test Details

• 57 tests across 14 describe blocks
• Mocks: fs-extra, js-yaml
• All tests passing

[nikolasdehor]

Covered by consolidated PR #426