Summary

• add a watched-repositories section to vigilante status
• summarize key watch-target metadata and current activity per repo in a compact, stable format
• cover the new section with focused status tests and update the README command description

Validation

• go test ./internal/app -run 'TestStatusCommand|TestWatchedRepoStatuses|TestGroupSessions|TestFormatSessionRow|TestIsPRTracking|TestIsStaleBlockedUsesConfiguredTimeout'
• go test ./internal/app (currently fails in unrelated existing test TestScanOncePausesWhenGitHubCoreRateLimitIsLowAndCommentsActiveIssues because its fake runner does not provide gh api user --jq .login)

Closes #270