Add a guide about Cross-Imports

[Gaic4o]

I'd like to propose creating a new documentation page about Cross-Imports — a recurring architectural issue in Feature-Sliced Design.

Before drafting the guide, I plan to review and summarize the relevant Telegram discussions, including:

• (Thread) About the supposed inevitability of cross-ports
• (Thread) About resolving cross-ports in entities
• (Thread) About cross-imports and responsibility
• (Thread) About imports between segments
• (Thread) About cross-imports inside shared

These threads contain real-world examples discussed by the community,
which, after some refinement, could serve as a strong foundation for an official guide.