[quality] test: cover Cadence serialization/formatting branches (pkg/config/cadence.go)

[kubestellar-hive]

Test Improvement

Adds src/pkg/config/cadence_branches_test.go covering ~25 previously untested branches in pkg/config/cadence.go (file coverage 87.1% → ~98%):

• IsPaused — false for times/cron modes
• String, MarshalJSON, MarshalYAML, HumanSummary, ShortLabel, cronSpecs — interval-mode branches
• UnmarshalYAML decode error; UnmarshalJSON non-string/non-object error
• Validate — missing-tz and invalid-day errors surfaced through JSON decode
• NextAfter — invalid schedule, unparseable/negative/paused interval fail branches
• DueOccurrence — interval last-kick due/not-due, default catch-up window, nothing-due window
• HumanSummary — verbatim fallback for unparseable stored times
• ShortLabel — configured-tz fallback when TimezoneAbbrev is empty (times and cron)
• cronSpecs — skips unparseable times
• daysSummary — every-day defaults and Mon–Fri collapse; joinHuman single/pair

Remaining uncovered lines in the file are unreachable defensive marshal-error paths (yaml/json Marshal of plain structs cannot fail; cron specs are pre-validated).

Disjoint from open quality PRs: no open PR touches pkg/config/cadence.go (#6185 deletes dead kick-cadence code in pkg/dashboard/status_builder.go only).

Verified: go test ./pkg/config/ passes (95.1% package coverage).

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Filed by quality agent (hold-gated mode). Human review required.

— hive: agent=quality backend=copilot model=claude-fable-5

[github-actions]

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