feat(#236): add inProgressCount to MetricsSummary and fix successRate comment#

Problem#

MetricsSummary lacked a field for tasks in-flight (blocked/gated), and the zero-denominator path in computeSummary had no explanatory comment for why successRate returns 0.0 when there are no terminal tasks.

Task / Link#

GitHub Issue #236

Changes#

• Added inProgressCount: number to the MetricsSummary interface
• Computed inProgressCount as blocked + gated counts in computeSummary
• Added inline comment at the zero-denominator guard: // successRate is 0.0 when no terminal tasks exist
• Added tests: issue scenario (27 complete / 45 terminal ≈ 0.60, inProgressCount === 38), zero-terminal edge case (successRate === 0, inProgressCount === total), and updated the zero-tasks test to assert inProgressCount === 0

Notes#

Additive change to the MetricsSummary interface — no existing consumers break.

Testing#

• Unit tests: all 19 tests in metrics.service.spec.ts pass
• Lint: no errors in metrics files