Admin: install parts, set time and weather; join without prompt

- VEHICLE: INSTALL for parts that are not installed - runs the game's own
  assembly (trigger "Assembly" like on load), so the part sits exactly on its
  pivot; synced to other players via FsmSync (MSCO_INSTALL)
- WORLD: time buttons (2-hour steps via the sun FSM's load path) and
  CLEAR / RAIN / THUNDERSTORM (weather front moved above the admin);
  sent to everyone as mod message "msco.world" (no server update needed)
- JOIN from the server browser/website connects right away in the main menu;
  server mods still ask before downloading

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

MSCO.csproj

@@ -97,6 +97,7 @@
     <Compile Include="PerfStats.cs" />
     <Compile Include="FsmDump.cs" />
     <Compile Include="VehicleAdmin.cs" />
+    <Compile Include="WorldAdmin.cs" />
     <Compile Include="ModApi.cs" />
     <Compile Include="ModLoader.cs" />
     <Compile Include="MenuBranding.cs" />