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)

addons/netfox/serializers/tickset-serializer.gd

@@ -0,0 +1,37 @@
+extends Object
+class_name _TicksetSerializer
+
+static func serialize(earliest_tick: int, latest_tick: int, active_ticks: _Set) -> PackedByteArray:
+	var buffer := StreamPeerBuffer.new()
+	var tickset_duration = latest_tick - earliest_tick
+
+	assert(latest_tick >= earliest_tick, "Tickset ends before it starts!")
+	assert(tickset_duration <= 255, "Tickset covers more than supported 255 ticks!")
+
+	buffer.put_u32(earliest_tick)
+	buffer.put_u8(tickset_duration)
+
+	for tick in active_ticks:
+		# Don't serialize before range
+		if tick < earliest_tick: continue
+		# Don't serialize past range
+		if tick > latest_tick: break
+		buffer.put_u8(tick - earliest_tick)
+
+	return buffer.data_array
+
+static func deserialize(bytes: PackedByteArray) -> Array:
+	var buffer := StreamPeerBuffer.new()
+	buffer.data_array = bytes
+
+	var earliest_tick := buffer.get_u32()
+	var tickset_duration := buffer.get_u8()
+	var latest_tick := earliest_tick + tickset_duration
+
+	var active_ticks := _Set.new()
+
+	while buffer.get_available_bytes() > 0:
+		var tick = earliest_tick + buffer.get_u8()
+		active_ticks.add(tick)
+
+	return [earliest_tick, latest_tick, active_ticks]

addons/netfox/serializers/tickset-serializer.gd.uid

@@ -0,0 +1 @@
+uid://b88vxloxp2wff