show tooltip for artifacts in the header bar

src/test/ConfigLoaderTest.cpp

@@ -88,6 +88,11 @@ TEST_CASE("ConfigLoader loads the committed bin/config/ configs end-to-end", "[c
     REQUIRE(*cfg.world.buildingBlocksTooltip ==
             "Spend building blocks to build; deliver them to the HQ to gain more.");
 
+    // Optional header artifact tooltip (REQ-UI-ARTIFACTS-TOOLTIP).
+    REQUIRE(cfg.world.artifactTooltip.has_value());
+    REQUIRE(*cfg.world.artifactTooltip ==
+            "Choose the artifact reward when destroying enemy stations; collect enough to win.");
+
     // Spot-check that a config-derived formula computes as expected.
     // threat_rate_formula = "x": evaluates to the input value.
     REQUIRE(cfg.world.waves.threatRateFormula.evaluate(1.0) == Approx(1.0));