Add sprint-stats, close-milestone skills and scripts to ai_initiative_marketing
> Follow-up to [ai_initiative#3586381](https://git.drupalcode.org/project/ai_initiative/-/work_items/3586381) (migration of AI Marketing Initiative to ai_initiative_marketing).
## Summary
Port the sprint management skills and scripts from `project/ai_initiative` to `project/ai_initiative_marketing`, and remove the now-obsolete Marketing issue templates from ai_initiative.
## Changes
### ai_initiative_marketing (this repo)
- Add `skills/sprint-stats/SKILL.md` -- sprint report generation skill
- Add `skills/close-milestone/SKILL.md` -- sprint-change workflow skill
- Add `scripts/run-sprint-stats.sh` -- sprint report generation script
- Add `scripts/run-close-milestone.sh` -- end-of-sprint workflow script
- Add `.gitignore` for generated `reports/` directory
- All project IDs updated to 212236 (`project/ai_initiative_marketing`)
### ai_initiative (sibling PR)
- Remove 5 Marketing issue templates (Blog Entry, Case Study, Generic, Video, Webinar) -- these already exist in ai_initiative_marketing
- Add Total/Average summary row to the Aggregate Statistics table in sprint-stats report
## Acceptance Criteria
- [ ] Sprint-stats and close-milestone skills work against ai_initiative_marketing milestones
- [ ] Marketing issue templates removed from ai_initiative
- [ ] Sprint report Aggregate Statistics table includes a bold Total/Average row
*Drafted with the assistance of AI (Claude Code / Opus 4.7).*
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