Phase 7: netfox + godot-jolt stack upgrade

Stack installed:
- netfox v1.35.3 (core + extras + noray + internals)
- godot-jolt v0.16.0-stable

Architecture:
- Server: ENet transport (works headless, no netfox deps)
- Client/Editor: netfox rollback (RollbackSynchronizer, TickInterpolator)

New/modified:
- docs/migration-netfox-plan.md — migration architecture
- scripts/network/network_manager.gd — netfox-aware ENet fallback
- scripts/network/player.gd — clean base player
- client/characters/player_netfox.gd — rollback player w/ WeaponManager
- client/characters/input/player_net_input.gd — BaseNetInput subclass
- client/characters/character/fps_character_controller.gd — netfox input feed
- client/weapons/ — weapon data, registry, TacticalWeaponHitscan, WeaponManager
- client/scripts/round_replicator.gd — client-side round state bridge
- server/scripts/round_manager.gd — improved state machine
- server/scripts/plugin_api/plugin_manager.gd — refined plugin system
- config: enemy_tag, ally_tag for meatball targeting

Removed: old C++ SimulationServer GDExtension (replaced by netfox rollback)

client/characters/input/player_net_input.gd

@@ -0,0 +1,29 @@
+## PlayerNetInput — netfox BaseNetInput subclass for the tactical shooter.
+##
+## Collects player input each network tick for the rollback system.
+## Referenced by RollbackSynchronizer's `input_properties`.
+##
+## This script is ONLY loaded from client scenes where netfox is active.
+
+extends "res://addons/netfox.extras/base-net-input.gd"
+class_name PlayerNetInput
+
+# Movement
+var move_direction: Vector3
+var look_yaw: float
+var look_pitch: float
+
+# Actions
+var jump: bool
+var sprint: bool
+var crouch: bool
+var shoot: bool
+var aim: bool
+
+# Weapon
+var weapon_slot: int = -1  # -1 = no change, 0-4 for slot index
+var reload: bool
+var use: bool  # interact / plant / defuse
+
+# Input sequence for reconciliation
+var input_sequence: int