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/encoder/snapshot-history-encoder.gd

@@ -0,0 +1,67 @@
+extends RefCounted
+class_name _SnapshotHistoryEncoder
+
+var _history: _PropertyHistoryBuffer
+var _property_cache: PropertyCache
+var _properties: Array[PropertyEntry]
+
+var _version := -1
+var _has_received := false
+
+static var _logger := NetfoxLogger._for_netfox("_SnapshotHistoryEncoder")
+
+func _init(p_history: _PropertyHistoryBuffer, p_property_cache: PropertyCache):
+	_history = p_history
+	_property_cache = p_property_cache
+
+func set_properties(properties: Array[PropertyEntry]) -> void:
+	if _properties != properties:
+		_version = (_version + 1) % 256
+		_properties = properties.duplicate()
+
+func encode(tick: int, properties: Array[PropertyEntry]) -> Array:
+	var snapshot := _history.get_snapshot(tick)
+	var data := []
+	data.resize(properties.size())
+
+	for i in range(properties.size()):
+		data[i] = snapshot.get_value(properties[i].to_string())
+	data.append(_version)
+
+	return data
+
+func decode(data: Array, properties: Array[PropertyEntry]) -> _PropertySnapshot:
+	var result := _PropertySnapshot.new()
+	var packet_version = data.pop_back()
+
+	if packet_version != _version:
+		if not _has_received:
+			# First packet, assume version is OK
+			_version = packet_version
+		else:
+			# Version mismatch, can't parse
+			_logger.warning("Version mismatch! own: %d, received: %s", [_version, packet_version])
+			return result
+
+	if properties.size() != data.size():
+		_logger.warning("Received snapshot with %d entries, with %d known - parsing as much as possible", [data.size(), properties.size()])
+
+	for i in range(0, mini(data.size(), properties.size())):
+		result.set_value(properties[i].to_string(), data[i])
+
+	_has_received = true
+
+	return result
+
+func apply(tick: int, snapshot: _PropertySnapshot, sender: int = -1) -> bool:
+	if tick < NetworkRollback.history_start:
+		# State too old!
+		_logger.error("Received full snapshot for %s, rejecting because older than %s frames", [tick, NetworkRollback.history_limit])
+		return false
+
+	if sender > 0:
+		snapshot.sanitize(sender, _property_cache)
+		if snapshot.is_empty(): return false
+
+	_history.set_snapshot(tick, snapshot)
+	return true