feat(ugc): models with no bricks are "empty", not failed

A model with no bricks has nothing to make: it gets its own state
(is_optimized = 3), isn't counted as a failure or retried, shows as Empty
on the UGC page (with its own filter and count), in the status and in
Prometheus, and its downloads answer 404 like HKX. State names come from
the enum (magic_enum). Migrations dlu/mysql/87 and dlu/sqlite/70 move the
rows that failed only because they had no bricks.

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

dDatabase/GameDatabase/ITables/IUgc.h

@@ -8,6 +8,8 @@
 #include <string_view>
 #include <vector>
 
+#include "magic_enum.hpp"
+
 class IUgc {
 public:
 	struct Model {
@@ -40,8 +42,23 @@ public:
 		PENDING = 0, // not made yet (or to be made again)
 		DONE = 1,    // the UGC server's files are made
 		FAILED = 2,  // gave up after the allowed attempts
+		EMPTY = 3,   // nothing to make: the model has no bricks (not a failure; never retried)
 	};
 
+	// A state's name for the dashboard, the API and metrics ("pending", "done", "failed", "empty")
+	static std::string ProcessStateName(eProcessState state) {
+		std::string name(magic_enum::enum_name(state));
+		for (auto& c : name) c = static_cast<char>(c >= 'A' && c <= 'Z' ? c - 'A' + 'a' : c);
+		return name.empty() ? "unknown" : name;
+	}
+
+	static std::optional<eProcessState> ParseProcessState(std::string_view text) {
+		for (const auto state : magic_enum::enum_values<eProcessState>()) {
+			if (ProcessStateName(state) == text) return state;
+		}
+		return std::nullopt;
+	}
+
 	// A row's processing state, for the UGC server and the dashboard
 	struct ProcessInfo {
 		LWOOBJID id{};