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/UgcJobs.h

@@ -0,0 +1,55 @@
+#pragma once
+
+#include <cstdint>
+#include <filesystem>
+#include <string>
+#include <string_view>
+#include <vector>
+
+#include "UgcBricks.h"
+#include "UgcRender.h"
+#include "UgcStorage.h"
+
+/**
+ * The work a UGC worker thread does for one item: everything from the stored LXFML (or a modular build's modules) to
+ * the finished files. No database, network or CDClient: the main thread gathers the input and stores the result.
+ */
+namespace UgcJobs {
+	struct Settings {
+		UgcRender::OptimizeOptions optimize;
+		UgcRender::IconOptions icon;
+		UgcRender::IconOptions modularIcon;
+	};
+
+	struct Outcome {
+		bool ok{};
+		std::string error;       // why it failed
+		std::string note;        // what was odd but not fatal (missing bricks, ...)
+		UgcStorage::Files files; // name -> bytes, when ok
+		bool aoBaked{};
+	};
+
+	// The client's download of `data` (`name` + ".gz" and ".checksum") added to `files`
+	void AddDownload(UgcStorage::Files& files, const std::string& name, const std::string& data);
+
+	// The LXFML of a ugc row's lxfml column (an sd0 stream, or plain LXFML); empty when it can't be read
+	std::string LxfmlFromBlob(const std::string& blob);
+
+	// A player model: the optimized .nif, its icon and its LXFML for download
+	Outcome ProcessModel(const std::string& blob, UgcBricks::BrickLibrary& library, const Settings& settings);
+
+	struct ModuleInput {
+		uint32_t lot{};
+		uint32_t partCode{};
+		std::string renderAsset; // RenderComponent.render_asset, relative to the client's res folder
+		std::string moduleXml;   // ModuleComponent.xml
+	};
+
+	struct ModularInput {
+		std::vector<ModuleInput> modules;
+		std::string buildXml; // ModularBuildComponent.xml of the modules' build type
+	};
+
+	// A modular build's icon, from its modules' meshes put together
+	Outcome ProcessModular(const ModularInput& input, const std::filesystem::path& res, const Settings& settings);
+}