Add patterns: Sponsor-Amplified Evangelism and Discovering Cross-Team Success Stories

[shrutibist]

Two new, related InnerSource patterns building on the previously submitted Sponsor Communication and Engagement pattern:

• Sponsor-Amplified Evangelism: using sponsors' own meetings as a distribution channel for program visibility, with a tested approach for planning cues and tracking portal-traffic impact.
• Discovering Cross-Team Success Stories: a programmatic technique for detecting real cross-team collaboration at scale by comparing contributor identity against team/BU mapping, used to source concrete case studies for the other two patterns.

[shrutibist]

The failing Link Checker check appears unrelated to this PR, it's flagging a 403 from oreilly.com elsewhere in the repo, not from my new file.