feat(editor): invert heights, fill entire tile with water, remove all water

- Invert Heights: flips terrain upside-down around midpoint (mountains
  become valleys and vice versa)
- Fill Entire Tile with Water: one-click fills all 256 chunks at the
  configured water height and liquid type
- Remove ALL Water: clears water from every chunk instantly
- Water panel now has three water operations: fill tile, remove under
  brush, remove all
- fillWater() and invertHeights() methods on TerrainEditor

tools/editor/editor_ui.cpp

@@ -1470,13 +1470,21 @@ void EditorUI::renderWaterPanel(EditorApp& app) {
             app.setWaterType(static_cast<uint16_t>(typeIdx));
 
         ImGui::Separator();
+        if (ImGui::Button("Fill Entire Tile with Water", ImVec2(-1, 0))) {
+            app.getTerrainEditor().fillWater(app.getWaterHeight(), app.getWaterType());
+            app.showToast("Tile filled with water");
+        }
         if (ImGui::Button("Remove Water Under Brush", ImVec2(-1, 0))) {
             auto& brush = app.getTerrainEditor().brush();
             if (brush.isActive()) {
                 app.getTerrainEditor().removeWater(brush.getPosition(), s.radius);
-                app.getEditorCamera(); // trigger dirty
             }
         }
+        if (ImGui::Button("Remove ALL Water", ImVec2(-1, 0))) {
+            for (int ci = 0; ci < 256; ci++)
+                app.getTerrainEditor().getTerrain()->waterData[ci].layers.clear();
+            app.showToast("All water removed");
+        }
 
         ImGui::Separator();
         ImGui::TextColored(ImVec4(0.5f, 0.8f, 1.0f, 1.0f), "Left-click to place water");

tools/editor/terrain_editor.cpp

@@ -860,6 +860,56 @@ void TerrainEditor::createHill(const glm::vec3& center, float radius, float heig
     dirty_ = true;
 }
 
+void TerrainEditor::invertHeights() {
+    if (!terrain_) return;
+    // Find midpoint
+    float minH = 1e30f, maxH = -1e30f;
+    for (int ci = 0; ci < 256; ci++) {
+        auto& chunk = terrain_->chunks[ci];
+        if (!chunk.hasHeightMap()) continue;
+        for (int v = 0; v < 145; v++) {
+            minH = std::min(minH, chunk.heightMap.heights[v]);
+            maxH = std::max(maxH, chunk.heightMap.heights[v]);
+        }
+    }
+    float mid = (minH + maxH) * 0.5f;
+    for (int ci = 0; ci < 256; ci++) {
+        auto& chunk = terrain_->chunks[ci];
+        if (!chunk.hasHeightMap()) continue;
+        for (int v = 0; v < 145; v++)
+            chunk.heightMap.heights[v] = mid - (chunk.heightMap.heights[v] - mid);
+        dirtyChunks_.push_back(ci);
+    }
+    for (int ci = 0; ci < 256; ci++) stitchEdges(ci);
+    dirty_ = true;
+}
+
+void TerrainEditor::fillWater(float height, uint16_t liquidType) {
+    if (!terrain_) return;
+    for (int ci = 0; ci < 256; ci++) {
+        auto& water = terrain_->waterData[ci];
+        if (water.layers.empty()) {
+            pipeline::ADTTerrain::WaterLayer wl;
+            wl.liquidType = liquidType;
+            wl.flags = 0;
+            wl.minHeight = height;
+            wl.maxHeight = height;
+            wl.x = 0; wl.y = 0; wl.width = 9; wl.height = 9;
+            wl.heights.assign(81, height);
+            wl.mask.assign(8, 0xFF);
+            water.layers.push_back(wl);
+        } else {
+            auto& wl = water.layers[0];
+            wl.liquidType = liquidType;
+            wl.minHeight = height;
+            wl.maxHeight = height;
+            std::fill(wl.heights.begin(), wl.heights.end(), height);
+        }
+        dirtyChunks_.push_back(ci);
+    }
+    dirty_ = true;
+}
+
 void TerrainEditor::thermalErosion(int iterations, float talusAngle) {
     if (!terrain_) return;
     float unitSize = CHUNK_SIZE / 8.0f;

tools/editor/terrain_editor.hpp

@@ -105,6 +105,12 @@ public:
     // Thermal erosion: material falls downhill based on angle of repose
     void thermalErosion(int iterations, float talusAngle);
 
+    // Invert terrain (flip heights around midpoint)
+    void invertHeights();
+
+    // Fill entire tile with water at a height
+    void fillWater(float height, uint16_t liquidType);
+
     // Import/export heightmap (raw 16-bit grayscale, 129x129)
     bool importHeightmap(const std::string& path, float heightScale);
     bool exportHeightmap(const std::string& path, float heightScale);