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/08-weapons-systems.md

@@ -136,4 +136,41 @@ Holstered → Equipping → Ready ⇄ Firing → Reloading → Ready
 
 ---
 
+## Multiplayer Networking
+
+### Category Authority Map
+| System | Authority | Client Prediction |
+|--------|-----------|-------------------|
+| `BP_WeaponBase` | Server-authoritative state machine | Client predicts fire animation/muzzle flash |
+| `BPC_AmmoComponent` | Server-authoritative ammo | Client predicts count; server corrects via OnRep |
+| `BPC_FirearmSystem` | Server performs trace/damage calc | Client predicts tracers; server hit result is canonical |
+| `BPC_MeleeSystem` | Server validates hit detection | Client predicts swing animation |
+| `BPC_ReloadSystem` | Server validates reload | Client predicts animation; server validates ammo state |
+| `BPC_RecoilSystem` | **Local only** | Recoil is cosmetic; no replication needed |
+| `BPC_DamageReceptionSystem` | Server calculates damage | HealthSystem is authoritative |
+| `BPC_HitReactionSystem` | Server triggers → multicast animation | All clients see flinch/stagger |
+| `BPC_CombatFeedbackComponent` | **Local only** | Hit markers, kill confirm are per-client |
+| `BPC_ShieldDefenseSystem` | Server validates block/parry | Shield state replicated |
+
+### Weapon Fire Flow (Multiplayer)
+```
+Client presses Fire:
+  1. Client predicts: play fire anim, muzzle flash, recoil immediately
+  2. Client calls Server_StartFire() RPC
+  3. Server validates: weapon state Ready, has ammo, not on cooldown
+  4. Server: trace/damage calc, consume ammo → RepNotify ammo to all
+  5. Server: Multicast fire FX to other clients
+  6. Client receives OnRep_Ammo → corrects if prediction was wrong
+```
+
+### Server RPCs
+- `Server_StartFire`, `Server_StopFire`, `Server_StartReload`, `Server_EquipWeapon`, `Server_HolsterWeapon`
+
+### Anti-Cheat
+- Server validates fire rate (timer between Server_StartFire calls must exceed weapon fire rate)
+- Server never trusts client damage calculations — always recalculates from weapon data
+- Server validates ammo count before allowing fire (prevents infinite ammo cheat)
+
+---
+
 *Developer Reference v1.0 — 08 Weapons Systems. Companion to docs/blueprints/08-weapons/ specs.*