Cycle completion chart ignores its date range and buckets by updated_at

[cavidelizade]

Summary

The cycle completion chart ignores the date range it's given and buckets completions by updated_at, so any later edit to a completed issue moves its completion bar to the edit day.

Where

CycleStore.CycleCompletionChart (apps/api/internal/store/cycle.go) takes startDate and endDate but the SQL never references them, so completions on any date are returned despite the "per day within the cycle's range" comment. It also buckets by TO_CHAR(i.updated_at, ...). There's no completed_at or activity-based date, so updated_at is standing in for completion time.

Repro

Complete an issue during the cycle, then edit its title a week later. The burnup chart shows the completion on the edit day, possibly outside the cycle window.

Fix

Filter by the passed date range, and bucket by an actual completion timestamp (a completed_at column or the state-change activity) rather than updated_at.

[cavidelizade]

Two separate problems here, and the second needs a schema decision, so noting the plan.

1. CycleCompletionChart takes startDate/endDate but the SQL never references them, so it returns completions on any date. That part is a clean fix (add the range to the WHERE).

2. It buckets by TO_CHAR(i.updated_at, ...), using updated_at as a stand-in for "when it was completed". There's no completed_at column and no state-change timestamp to key off, so any later edit to a completed issue moves its bar. Fixing this properly means either adding a completed_at column (set when an issue enters a completed-group state) or deriving the date from issue_activities. That's a data-model decision I didn't want to make unilaterally.

If you're happy with adding completed_at, I'll do the migration + the write path + rework the chart to use it (and apply the date range). Let me know which direction you prefer.