feat(editor): status bar shows active biome

Adds a public EditorApp::getActiveBiome() accessor and renders the
biome name in the status bar between the tile coords and the
dirty marker. So the bar reads, e.g., "[Sculpt] mymap [32,32]
Forest *" — at a glance the user knows what biome the painting/
auto-paint passes will use.

Useful especially after creating a new terrain: the biome
selection previously only mattered at create time + during
"Generate Complete Zone", with no visible feedback that it was
remembered.

tools/editor/editor_app.hpp

@@ -207,6 +207,9 @@ private:
     // reads this so subsequent generations honor the active biome instead of
     // reapplying the same hardcoded heightband textures every time.
     Biome activeBiome_ = Biome::Grassland;
+public:
+    Biome getActiveBiome() const { return activeBiome_; }
+private:
 
     // "Click on terrain to place crater" mode. The Crater button arms this
     // with the user's chosen radius/depth/rim; the next left-click on

tools/editor/editor_ui.cpp

@@ -3119,8 +3119,9 @@ void EditorUI::renderStatusBar(EditorApp& app) {
         if (app.hasTerrainLoaded()) {
             bool dirty = app.getTerrainEditor().hasUnsavedChanges() ||
                          app.hasUnsavedNonTerrainChanges();
-            ImGui::Text("[%s] %s [%d,%d]%s", m, app.getLoadedMap().c_str(),
+            ImGui::Text("[%s] %s [%d,%d] %s%s", m, app.getLoadedMap().c_str(),
                         app.getLoadedTileX(), app.getLoadedTileY(),
+                        getBiomeName(app.getActiveBiome()),
                         dirty ? " *" : "");
             ImGui::SameLine(vp->Size.x * 0.35f);
             ImGui::Text("Obj:%zu NPC:%zu Q:%zu",