Add `issue_usage` table with columns for user_uid, tokens, cost, and latency metrics, including a unique index on user_uid. Wire `accumulate_usage` into `enhance_ticket` and `generate_plan` to capture per-request AI usage, persist totals via `add_issue_usage` in both `IssueCreateService` and `PlanningReportService`, and expose aggregated usage as metric cards through `IssueTrackerService.collect_metrics`. Update planning API docs summary to reflect the new phased implementation document format.
