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/blueprints/10-adaptive/97_BPC_MemoryDriftSystem.md

@@ -195,7 +195,7 @@ flowchart TD
 - MutationRegistry is populated per level — each level defines which rooms can mutate and how
 - DriftIntensity is ramped up by the adaptive director as the game progresses
 - For non-horror games, leave MutationRegistry empty to disable the system
-- Room tags are defined in GI_GameTagRegistry — add project-specific rooms there
+- Room tags are defined in DA_GameTagRegistry — add project-specific rooms there
 - Extend DA_RoomMutation with new mutation types (actor spawn, light change, sound trigger, etc.)
 
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