Add tooltip for building blocks in header bar

src/test/ConfigLoaderTest.cpp

@@ -83,6 +83,11 @@ TEST_CASE("ConfigLoader loads the committed bin/config/ configs end-to-end", "[c
     REQUIRE(cfg.world.rallyOrbitRadius_tiles == Approx(5.0));
     REQUIRE(cfg.world.scrapPerThreat == Approx(1.0));
 
+    // Optional header building blocks tooltip (REQ-UI-BLOCKS-TOOLTIP).
+    REQUIRE(cfg.world.buildingBlocksTooltip.has_value());
+    REQUIRE(*cfg.world.buildingBlocksTooltip ==
+            "Spend building blocks to build; deliver them to the HQ to gain more.");
+
     // 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));