Closes #921
## Product slice
- Adds **File as related issue** to mobile checklist-step management.
- Prefills capture with repository, normalized step title, and canonical parent backlink.
- Links the confirmed child back into only the selected parent checklist step with revision checking.
- Carries parent context through durable issue delivery and surfaces partial-success conflicts without recreating the child.
- Keeps core runtime under its 99 KiB gzip budget by moving issue outbox into the eager workflow chunk.
## Verification
- `python3 -m pytest tests/ -q` — 1773 passed, 1 skipped
- release bundle checksum verified
- Playwright release journey — 1 passed
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Closes #921
Product slice
Verification
python3 -m pytest tests/ -q— 1773 passed, 1 skipped