Expand IKEA known instance in InnerSource Hackathon pattern

[rrrutledge]

Summary

• Replaces the bare **IKEA** (Ingka Group) placeholder with a full description of IKEA's hackathon experience, matching the level of detail in the Aerospace Corporation entry
• Details sourced from Shanmugapriya Manoharan's December 2024 InnerSource Commons community call talk: Hackathon: A Fun and safe approach to get started with InnerSource
• Removes a redundant Acknowledgments entry (Shanmugapriya is already listed as Author)

Content added

• Virtual, one-day format with a few extra days for submission
• Two participation categories (new project vs. contribute to existing), including the maintainer pre-work requirement
• Judging panel drawn from different business areas, all InnerSource advocates
• Outcomes: participation from 6 countries, contributions to ~6 InnerSource projects, ~50% growth in the InnerSource project landscape, one project identified as an open-sourcing candidate
• Reached engineers who would not have engaged through normal awareness campaigns

Test plan

• Read through the updated Known Instances section and confirm the IKEA entry reads consistently with the Aerospace Corporation entry

🤖 Generated with Claude Code

[spier]

@spriya-m would you have time to review this, to check if this represents you experience correctly?

[rrrutledge]

I sent a DM to @spriya-m to ask for a review.

[spier]

I have only pushed some changes to get the spell checker to pass. Plus some formatting changes for the Known Instances section, to make it easier to read once published to the book.

[spier]

@rrrutledge I assume you did not get a review on this yet, did you?

Also by now this PR diverged from the mainline, so in either case one would have to resolve the merge conflicts first, I am afraid :(

[spier]

@rrrutledge are you happy for this PR to be merged, or would you like to wait for review from @spriya-m?

[rrrutledge]

@spier Happy for this to be merged as-is — no need to wait on further review from Shanmugapriya

[spier]

Changes are now live here (might have to force-refresh the page to show the new content):
https://patterns.innersourcecommons.org/p/innersource-hackathon#known-instances