Refactor GameplayTag documentation and implementation

- Updated references from GI_GameTagRegistry to DA_GameTagRegistry in architecture overview and implementation patterns documentation.
- Added new Blueprint specification for GI_StarterGameInstance, detailing its purpose, configuration, and integration pattern.
- Introduced DA_GameTagRegistry Blueprint specification, centralizing GameplayTag management and providing functions for tag validation and logging.
- Created documentation for the Starter GameInstance, outlining its role in the project setup and how other systems can integrate with it.

docs/developer/implementation-patterns.md

@@ -243,7 +243,7 @@
 
 **Key Rules:**
 - Framework tags use `Framework.` prefix; project tags use `Game.` prefix
-- All tags documented in `GI_GameTagRegistry`
+- All tags documented in `DA_GameTagRegistry`
 - Never use `FName` or `FString` for state — always GameplayTags
 
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