Fresh start: replace with naxIO/netfox-cs-sample foundation

Complete replacement of the tactical-shooter project with the
netfox-cs-sample (MIT) — a CS 1.6 inspired multiplayer FPS built
with Godot 4 and netfox.

## What's new
- Full CS-style gameplay: teams (T/CT), rounds, economy, buy menu
- 6 weapons: Knife, Glock, USP, AK-47, M4A1, AWP
- Bomb plant/defuse with 2 bombsites
- Flashbang & smoke grenades
- Proper netfox rollback netcode at 64 tick
- Network popup UI for host/join
- HUD, crosshair, round timer, scoreboard
- All netfox singletons registered as autoloads (works in exported builds)

## Architecture
- Listen-server (host from client, no dedicated server binary)
- Multiplayer-fps game lives at examples/multiplayer-fps/
- Netfox addons registered as autoloads for exported build compat
- Godot 4.7 with Forward+ renderer

## Removed
- Old headless-server architecture (client_main, server_main, player.gd, etc.)
- Custom netfox bootstrap with ENet fallback
- Old ChaffGames FPS template (2,420 lines, 844 KB)
- SimulationServer GDExtension stub
- Godot-jolt physics (netfox sample uses default Godot physics)
- Duplicate weapon_data.gd, anti_cheat.gd, round_manager.gd, etc.
- Server browser API Python venv (87 MB)
- test_range map and modular assets

## Preserved
- Git history
- Server config at config/default_server_config.cfg
- Windows export preset
- Build directory (gitignored)

Co-authored-by: naxIO <naxIO@users.noreply.github.com>

docs/upgrading.md

@@ -0,0 +1,50 @@
+# Upgrading netfox
+
+Improvements are fixes are added to netfox with time, based on user feedback,
+resulting in newer versions. This page is inteded to help you with upgrading
+your game to a newer netfox version.
+
+## General advice
+
+### Have a backup
+
+**Make sure to have a backup** of your project before upgrading. While most
+often an addon update should be harmless, it is a good practice to backup your
+project regularly, and specifically before risky changes.
+
+### Disable the addon(s)
+
+Before upgrading, disable the netfox addon(s) in your project, in Project
+Settings. After the upgrade, enable the addon(s) again.
+
+This helps with cases where an autoload or a project setting is changed.
+
+## Version-specific steps
+
+This section has version-specific entries where extra actions might be
+necessary. Versions where the general advice holds are left out.
+
+Make sure to apply all the steps between the versions, e.g. if you're updating
+from 1.0.0 to 1.3.0, refer to the sections between the two versions, in this
+case v1.1.1. If there are no sections here for your version range, that means
+that the upgrade should need no extra action, aside from replacing the old
+netfox addon(s) with the new one(s).
+
+### Unreleased
+
+* `StateSynchronizer.full_state_interval` is deprecated - use project settings
+* `StateSynchronizer.diff_ack_interval` is deprecated and is ignored
+* `RollbackSynchronizer.full_state_interval` is deprecated - use project
+  settings
+* `RollbackSynchronizer.diff_ack_interval` is deprecated and is ignored
+* `RollbackSynchronizer.enable_input_broadcast` is deprecated - use project
+  settings
+* `NetworkRollback.register_rollback_input_submission()` is deprecated and does
+  nothing
+* `NetworkRollback.free_input_submission_data_for()` is deprecated and does
+  nothing
+
+### v1.1.1
+
+* Remove `Interpolators` from the project autoloads, it's a static class now.
+