Feature: option to turn off automatic tank model loading

Lets people on limited data stop the Tankopedia from downloading 3D models automatically.

- Added an Automatically load 3D models switch to the settings page, on by default
- When off, the tank page hero shows a Load 3D model button where the loading bar sits
- Held back every model download on the tank page until requested, including the dynamic armor switcher and the gun flexibility visualizer
- Wrapped the tank sandbox in its own suspense boundary so the loading bar shows real progress instead of the whole page waiting on the model
- Measured loading progress from when each loading bar appears so it always starts empty
- Added the English strings; other languages fall back until translated

Fixes #311

packages/i18n/strings/en.json

@@ -215,6 +215,7 @@
       "title": "Settings",
       "description": "Change BlitzKit settings",
       "dev_mode": "Development mode",
+      "auto_load_models": "Automatically load 3D models",
       "language": "Language"
     },
 
@@ -458,6 +459,8 @@
         },
 
         "sandbox": {
+          "load_model": "Load 3D model",
+
           "poses": {
             "hull_down": "Hull down",
             "face_hug": "Face hug",