feat: Add multiplayer networking architecture and documentation updates

- Updated Master Blueprint Index to include Multiplayer Networking support.
- Added detailed Multiplayer Networking sections across all developer documentation (01-11).
- Introduced authority maps, key patterns, and RPC guidelines for each system.
- Established a comprehensive multiplayer networking architecture document outlining core principles, replication strategies, and anti-cheat considerations.
- Enhanced UI documentation to clarify local-only behavior and binding to replicated dispatchers.
- Implemented client prediction strategies and RPC naming conventions for consistency across the framework.

docs/developer/implementation-patterns.md

@@ -292,4 +292,96 @@
 
 ---
 
+## Multiplayer Networking Patterns
+
+### Pattern 11: Server Authority Gate
+
+**When to Use:** Every function that modifies replicated state.
+
+**Blueprint Implementation:**
+```
+[Function: ApplyDamage(DamageEvent)]
+  Switch HasAuthority
+    Authority:
+      → Execute authoritative logic (damage calc, health modification)
+      → Fire dispatchers
+    Remote:
+      → Return (client cannot modify replicated state directly)
+      → Client calls Server_ RPC to request the change
+```
+
+**Key Rule:** Never modify a replicated variable without `HasAuthority()` check.
+
+### Pattern 12: Server RPC Wrapper
+
+**When to Use:** Client needs to request a state change from the server.
+
+**Blueprint Implementation:**
+```
+[Client Event Graph — Input: Interact pressed]
+  → Call Server_Interact(TargetActor)  // RPC: Run on Server, Reliable
+
+[Server RPC: Server_Interact(TargetActor)]
+  Switch HasAuthority
+    Authority:
+      → Validate distance, conditions
+      → Call I_Interactable.Execute_OnInteract(TargetActor, Instigator)
+      → State changes replicate automatically
+```
+
+**Naming:** All Server RPCs prefixed with `Server_`.
+
+### Pattern 13: OnRep Dispatcher Relay
+
+**When to Use:** Any replicated variable that should trigger the same effects as single-player.
+
+**Blueprint Implementation:**
+```
+[Variable: CurrentHealth]
+  Replication: Replicated Using OnRep_CurrentHealth
+
+[Function: OnRep_CurrentHealth]
+  → Broadcast OnHealthChanged(OldHealth, CurrentHealth, Delta)
+  → UI, audio, effects react exactly as in single-player path
+  → No multiplayer-specific code in consumer systems
+```
+
+**Key Rule:** `OnRep_` fires the SAME dispatcher the SP mutation code fires. Zero consumer changes needed.
+
+### Pattern 14: Client Prediction with Correction
+
+**When to Use:** Actions that need instant feedback (firing, using items, interacting).
+
+**Blueprint Implementation:**
+```
+[Client: Input → Fire pressed]
+  → Client prediction: play fire animation, muzzle flash, reduce ammo display
+  → Call Server_StartFire()
+
+[Server: Server_StartFire()]
+  → Validate weapon state, ammo, cooldown
+  → If valid: execute authoritative fire logic, consume ammo
+  → If invalid: log warning, return (client will be corrected via OnRep)
+
+[Client: OnRep_Ammo]
+  → If server count matches client prediction: no visible change
+  → If different: correct ammo display, stop fire animation
+```
+
+### Pattern 15: Multicast for Cosmetic Events
+
+**When to Use:** Server needs to trigger a cosmetic-only event on all clients.
+
+**Blueprint Implementation:**
+```
+[Server: Explosion triggered]
+  → Multicast_PlayExplosionFX(Location, Radius)
+  → All clients play VFX, SFX, camera shake locally
+  → No replication of individual particles
+```
+
+**Key Rule:** Multicast is for **cosmetic only** — never use for state changes. State changes replicate via variable RepNotify.
+
+---
+
 *Implementation Patterns v1.0 — Reference when building blueprint specs into UE5 Blueprint assets.*