show tooltip for artifacts in the header bar

src/lib/config/ConfigLoader.cpp

@@ -279,6 +279,12 @@ WorldConfig ConfigLoader::loadWorld(const std::string& path)
         cfg.buildingBlocksTooltip = *tip;
     }
 
+    if (const std::optional<std::string> tip =
+            tbl["world"]["artifact_tooltip"].value<std::string>())
+    {
+        cfg.artifactTooltip = *tip;
+    }
+
     cfg.regions.asteroidWidth_tiles     = static_cast<int>(requireInt(tbl["regions"]["asteroid_width_tiles"],      file, "regions.asteroid_width_tiles"));
     cfg.regions.playerBufferWidth_tiles = static_cast<int>(requireInt(tbl["regions"]["player_buffer_width_tiles"], file, "regions.player_buffer_width_tiles"));
     cfg.regions.contestZoneWidth_tiles  = static_cast<int>(requireInt(tbl["regions"]["contest_zone_width_tiles"],  file, "regions.contest_zone_width_tiles"));

src/lib/config/WorldConfig.h

@@ -82,6 +82,10 @@ struct WorldConfig
     // (REQ-UI-BLOCKS-TOOLTIP). Presentation-only; the simulation ignores it.
     std::optional<std::string> buildingBlocksTooltip;
 
+    // Optional hover-tooltip for the header artifact count display
+    // (REQ-UI-ARTIFACTS-TOOLTIP). Presentation-only; the simulation ignores it.
+    std::optional<std::string> artifactTooltip;
+
     WorldRegions regions;
     WorldExpansion expansion;
     WorldPush push;