feat: UGC server that makes and serves player models' meshes and icons

A new server (dUgcServer, started by master with enable_ugc_server=1) that
takes unprocessed ugc and ugc_modular_build rows from the database and makes
what the client downloads with UGCUSE3DSERVICES: an optimized NIF (hidden
faces removed, ambient occlusion baked into vertex colors) and a 128px DDS
icon for player models, rendered by a software rasterizer from the client's
LDD brick primitives, and icons for cars and rockets assembled from their
modules per ModularBuildComponent/ModuleComponent. It serves them, with the
models' LXFML, over HTTP in the client's UGCC<dc>/3DOPTIMIZED and
IMAGE128DDS layout with .gz and .checksum files, and keeps its folder under
a size cap.

Processing state lives in ugc.is_optimized plus new processed_at,
process_attempts and process_error columns (and the same on
ugc_modular_build). ServiceType::UGC is appended. NifFile moves to dCommon
and records named node transforms for the modules' attach points.

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

dUgcServer/UgcCdClient.h

@@ -0,0 +1,12 @@
+#pragma once
+
+#include <string>
+
+#include "UgcJobs.h"
+
+// What the UGC server reads from the CDClient (main thread only: the CDClient connection isn't shared with workers)
+namespace UgcCdClient {
+	// A modular build's modules (ugc_modular_build.ldf_config) with their render assets and module data, and the
+	// ModularBuildComponent of their build type; false and `error` when it can't be put together
+	bool GatherModular(const std::string& modules, UgcJobs::ModularInput& input, std::string& error);
+}