feat(editor): height clamp tool for controlled terrain range

- Clamp Heights: sets min/max height bounds across entire tile
  (DragFloatRange2 slider for min/max, -500 to 2000 range)
- Useful workflow: Generate noise → Smooth → Clamp to desired range
- Prevents terrain from going underground or too high
- All affected chunks marked dirty for mesh regeneration

tools/editor/editor_ui.cpp

@@ -392,8 +392,15 @@ void EditorUI::renderBrushPanel(EditorApp& app) {
                 app.getTerrainEditor().smoothEntireTile(smoothPasses);
                 app.showToast("Tile smoothed");
             }
+            ImGui::Separator();
+            static float clampMin = 0.0f, clampMax = 500.0f;
+            ImGui::DragFloatRange2("Clamp Range", &clampMin, &clampMax, 1.0f, -500.0f, 2000.0f);
+            if (ImGui::Button("Clamp Heights", ImVec2(-1, 0))) {
+                app.getTerrainEditor().clampHeights(clampMin, clampMax);
+                app.showToast("Heights clamped");
+            }
             ImGui::TextColored(ImVec4(0.6f, 0.6f, 0.6f, 1),
-                "Generate terrain, then smooth for natural look");
+                "Generate, smooth, then clamp for controlled range");
         }
 
         ImGui::Separator();

tools/editor/terrain_editor.cpp

@@ -652,6 +652,27 @@ void TerrainEditor::smoothEntireTile(int iterations) {
     dirty_ = true;
 }
 
+void TerrainEditor::clampHeights(float minH, float maxH) {
+    if (!terrain_) return;
+    for (int ci = 0; ci < 256; ci++) {
+        auto& chunk = terrain_->chunks[ci];
+        if (!chunk.hasHeightMap()) continue;
+        bool modified = false;
+        for (int v = 0; v < 145; v++) {
+            float absH = chunk.position[2] + chunk.heightMap.heights[v];
+            if (absH < minH) {
+                chunk.heightMap.heights[v] = minH - chunk.position[2];
+                modified = true;
+            } else if (absH > maxH) {
+                chunk.heightMap.heights[v] = maxH - chunk.position[2];
+                modified = true;
+            }
+        }
+        if (modified) dirtyChunks_.push_back(ci);
+    }
+    dirty_ = true;
+}
+
 void TerrainEditor::applyErode(float dt) {
     float factor = std::min(1.0f, brush_.settings().strength * dt * 0.3f);
 

tools/editor/terrain_editor.hpp

@@ -57,6 +57,9 @@ public:
     // Global smooth pass across entire tile (N iterations)
     void smoothEntireTile(int iterations);
 
+    // Clamp all heights to a min/max range
+    void clampHeights(float minH, float maxH);
+
     // Import/export heightmap (raw 16-bit grayscale, 129x129)
     bool importHeightmap(const std::string& path, float heightScale);
     bool exportHeightmap(const std::string& path, float heightScale);