Single-binary race loop: menu -> race -> menu in one process

WinMain now wraps the engine block in a loop: when a front-end-launched
mission ends under the local console, the setup screen comes back in the
same process instead of exiting (the arcade relaunch-per-mission model).
Replaces the CreateProcess self-respawn - required for Steam, where the
lobby and sockets must survive across races.

Second-cycle re-init crash fixed: d3d_OBJECT kept a static texture cache
keyed by filename, so race 2 got IDirect3DTexture9 pointers created on
race 1 destroyed device and died at first draw (DrawMesh AV). The cache
is now flushed in ~DPLRenderer before the device is released, and
ParticleEngine::Initialize drops particles left over from the previous
mission. Verified: three consecutive 30s races in one PID, each stopped
on time by the console with final scores collected.

Also: L4CONSOLELEN env override for test-length races, and the console
exposes MissionCompleted() for the loop.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

MUNGA_L4/L4D3D.cpp

@@ -277,6 +277,17 @@ L4TEXOP d3d_OBJECT::LoadTexture(LPDIRECT3DDEVICE9 device, const char *fileName)
 	return texOp;
 }
 
+void d3d_OBJECT::FlushTextureCache()
+{
+	stdext::hash_map<std::string, L4TEXOP>::iterator iter;
+	for (iter = mTextureCache.begin(); iter != mTextureCache.end(); ++iter)
+	{
+		if ((*iter).second.texture != NULL)
+			(*iter).second.texture->Release();
+	}
+	mTextureCache.clear();
+}
+
 d3d_OBJECT::d3d_OBJECT(LPDIRECT3DDEVICE9 device, int vertCount)
   : mDevice(device),
 	mVertCount(vertCount),