Add fetcher_test.go covering: service creation, start/pause lifecycle,
calculatePriority scoring for all label types, label query construction
with custom and default labels, gh CLI JSON parsing for both list and
single-issue endpoints, channel backpressure when issuesCh is full,
fetchAll with no repos configured, and missing binary error handling.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
