Generalize Reed product positioning

[is2b007]

Summary

• lead with Reed as an offline-first narrative design and production workspace for branching games
• describe the full localization and game-export surface before individual integrations
• position Pixel Crushers as an optional deep graph integration instead of Reed's product identity
• update the product brief from the original five-language scope to the current 47-language BCP 47 catalog

Verification

• documentation-only change
• git diff --check
• audited public descriptions for the previous Unity/Pixel Crushers-first wording