extract loadUnlocks into ConfigLoaderUnlocks.cpp

Finishes the ConfigLoader.cpp domain split. ConfigLoader.cpp now holds
only the cross-domain validateUnlocks pass and loadFromDirectory
orchestrator, as intended — everything else lives in its own
ConfigLoader<Domain>.cpp. Pure move; no logic change.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YHcUerKAZKWNvSKJxYKbnG

src/lib/config/ConfigLoaderUnlocks.cpp

@@ -0,0 +1,62 @@
+#include "ConfigLoader.h"
+
+#include <string>
+#include <utility>
+
+#include "toml.hpp"
+
+#include "TomlHelpers.h"
+
+UnlocksConfig ConfigLoader::loadUnlocks(const std::string& path)
+{
+    const std::string file = "unlocks.toml";
+    toml::table tbl = parseFile(path, file);
+
+    UnlocksConfig cfg;
+    if (!tbl.contains("unlock"))
+    {
+        return cfg;
+    }
+
+    const toml::array& arr = requireArray(tbl["unlock"], file, "unlock");
+
+    for (std::size_t i = 0; i < arr.size(); ++i)
+    {
+        const std::string elemPath = "unlock[" + std::to_string(i) + "]";
+        const toml::table* ut = arr[i].as_table();
+        if (ut == nullptr)
+        {
+            throw makeError(file, elemPath, "not a table");
+        }
+        toml::table& mt = const_cast<toml::table&>(*ut);
+
+        UnlockGroupDef def;
+        def.id           = requireString(mt["id"], file, elemPath + ".id");
+        def.stationLevel = static_cast<int>(
+            requireInt(mt["station_level"], file, elemPath + ".station_level"));
+        if (mt.contains("requires"))
+        {
+            def.requiredGroupIds = requireStringArray(mt["requires"], file, elemPath + ".requires");
+        }
+        if (mt.contains("ships"))
+        {
+            def.ships = requireStringArray(mt["ships"], file, elemPath + ".ships");
+        }
+        if (mt.contains("modules"))
+        {
+            def.modules = requireStringArray(mt["modules"], file, elemPath + ".modules");
+        }
+        if (mt.contains("buildings"))
+        {
+            def.buildings = requireStringArray(mt["buildings"], file, elemPath + ".buildings");
+        }
+        if (mt.contains("recipes"))
+        {
+            def.recipes = requireStringArray(mt["recipes"], file, elemPath + ".recipes");
+        }
+
+        cfg.groups.push_back(std::move(def));
+    }
+
+    return cfg;
+}