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/architecture/bpc-statemanager.md

@@ -452,7 +452,7 @@ HasActionFlag(Tag: GameplayTag) → Boolean
 4. Populate default `GatingRules` from `DA_StateGatingTable` if assigned
 5. Bind to `GI_GameFramework.OnGamePhaseChanged` (for game-phase-gated rules)
 6. Bind to `BPC_HealthSystem.OnDeath` (auto-call `ForceStateChange(Dead)`)
-7. Register with `GI_GameTagRegistry` for tag-based queries
+7. Register with `DA_GameTagRegistry` for tag-based queries
 8. Bind to `BPC_HealthSystem.OnHealthChanged` → call `EvaluateInjuryState()`
 9. Bind to `BPC_StressSystem.OnStressTierChanged` → recalculate heart rate
 10. Bind to `BPC_StaminaSystem.OnExhaustionStateChanged` → recalculate heart rate