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/README.md

@@ -0,0 +1,37 @@
+# netfox
+
+The core addon of [netfox], providing responsive multiplayer features for the
+[Godot Engine].
+
+## Features
+
+* ⏲️  Synchronized time
+  * Runs game logic at a fixed, configurable tickrate
+  * Time synchronized to game host
+* 🧈 State interpolation
+  * Render 24fps tickrate at buttery smooth 60fps or more
+  * Add a `TickInterpolator` node and it just works
+* 💨 Lag compensation with CSP
+  * Implement responsive player motion with little to no extra code
+  * Just use the `RollbackSynchronizer` node for state synchronization
+
+## Install
+
+See the root [README](../../README.md).
+
+## Usage
+
+See the [docs](https://foxssake.github.io/netfox/).
+
+## License
+
+netfox is under the [MIT license](LICENSE).
+
+## Issues
+
+In case of any issues, comments, or questions, please feel free to [open an issue]!
+
+[netfox]: https://github.com/foxssake/netfox
+[source]: https://github.com/foxssake/netfox/archive/refs/heads/main.zip
+[Godot engine]: https://godotengine.org/
+[open an issue]: https://github.com/foxssake/netfox/issues