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/UgcRender.h

@@ -0,0 +1,56 @@
+#pragma once
+
+#include <cstdint>
+#include <vector>
+
+#include <glm/glm.hpp>
+
+#include "UgcModel.h"
+
+/**
+ * A small software rasterizer (no GPU or display needed) for what the UGC server draws: the icons, and the renders
+ * from many directions that find the faces nobody can see and bake ambient occlusion into the vertex colors.
+ */
+namespace UgcRender {
+	// 8-bit RGBA, rows top to bottom, not premultiplied
+	struct Image {
+		int width{};
+		int height{};
+		std::vector<uint8_t> rgba;
+	};
+
+	struct IconOptions {
+		int size{ 128 };
+		int supersample{ 4 };
+		float yawDegrees{ 35.0f };   // camera around the model, from +Z towards +X
+		float pitchDegrees{ 25.0f }; // camera above the model
+		float fovDegrees{ 30.0f };
+		float margin{ 1.03f };       // 1 fills the icon, more leaves a border
+		glm::mat4 modelRotation{ 1.0f }; // applied to the model before the camera looks at it
+	};
+
+	// The model drawn from the icon's camera, framed to fit, on a transparent background
+	Image RenderIcon(const UgcModel::Model& model, const IconOptions& options);
+
+	struct OptimizeOptions {
+		int resolution{ 1024 };   // of each direction's render
+		bool removeHidden{ true };
+		bool bakeAo{ true };
+		float aoStrength{ 0.6f }; // 0 leaves the colors, 1 makes fully hidden corners black
+	};
+
+	struct OptimizeResult {
+		size_t trianglesBefore{};
+		size_t trianglesRemoved{};
+	};
+
+	/**
+	 * Renders the opaque mesh from 42 directions around it: triangles that show in none of them are removed (with a
+	 * conservative test, so small visible ones stay), and each vertex's share of the directions it can be seen from
+	 * darkens its color (ambient occlusion). Transparent bricks hide nothing but are darkened too.
+	 */
+	OptimizeResult Optimize(UgcModel::Model& model, const OptimizeOptions& options);
+
+	// The 42 directions Optimize renders from (an icosahedron's corners and edge centres), unit length
+	std::vector<glm::vec3> SphereDirections();
+}