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/architecture-overview.md

@@ -78,7 +78,7 @@ No hardcoded values. Every configuration lives in Data Assets (`DA_ItemData`, `D
 Widgets display data from gameplay systems but never own game state. They bind to event dispatchers (`OnHealthChanged` → update health bar) and call functions (`UseItem()`) — but never store authoritative data.
 
 ### 5. GameplayTags for State, Not Booleans
-No `bIsDead`, `bIsHidden`, `bIsInCombat` booleans. Everything is a GameplayTag compared via `HasTag()` / `MatchesTag()`. Tags are documented in `GI_GameTagRegistry`.
+No `bIsDead`, `bIsHidden`, `bIsInCombat` booleans. Everything is a GameplayTag compared via `HasTag()` / `MatchesTag()`. Tags are documented in `DA_GameTagRegistry`.
 
 ### 6. Single Audio Entry Point (SS_AudioManager)
 Never call `UGameplayStatics::PlaySound*` directly. All audio routes through `SS_AudioManager` which manages 4 MetaSound buses (SFX, Ambience, Music, Dialogue → Master Bus). Room acoustics switch automatically via `BP_RoomAudioZone` triggers.