feat(kanban): make Done-card results obvious

[teknium1]

Summary

Done Kanban cards now surface their final result, child-task outcomes, and durable attachments directly in the drawer.

Built on @iborazzi's contribution in #41830, with the stale parent detection fixed and the API shape simplified to reuse existing fields.

Changes

• Renders task.result, falling back to the full latest run summary when workers use the normal kanban_complete(summary=...) handoff.
• Shows an explicit empty-result message for Done cards without either source.
• Detects parent/orchestrator cards from detail-level links.children, fixing the original PR's unreachable link_counts branch.
• Returns compact child result rows from the detail endpoint: id, title, status, result, and latest summary.
• Adds a Child Results section with one-click navigation into each child card.
• Keeps durable task attachments immediately beside the final result.
• Avoids a redundant final_result API alias; the UI resolves the existing result and latest_summary fields directly.

Closes #41820.

Validation

Check	Result
Kanban dashboard plugin tests	110 passed
API E2E	Parent summary and child summaries returned correctly
Live dashboard	Final Result, Child Results, and parent→child Open navigation verified
JavaScript syntax / diff checks	Passed

Attribution

@iborazzi's original commit is preserved in git history. The follow-up fixes parent detection, adds child-result retrieval/navigation, and removes the duplicate API alias.

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