feat: add surface exclusions panel and functionality

- Introduced a new section in the UI for surface exclusions, allowing users to exclude triangles from displacement using brush and bucket fill tools.
- Implemented brush type switching (single and radius) and radius control for the brush tool.
- Added functionality for bucket fill with a threshold angle to control the fill area.
- Integrated exclusion weights into the displacement algorithm to ensure excluded faces are handled correctly during subdivision.
- Created adjacency and centroid calculations for triangles to support the bucket fill operation.
- Developed overlay geometries for visual feedback on excluded faces and hover previews.
- Enhanced the CSS for the new exclusion tools and their layout in the UI.

index.html

@@ -109,7 +109,7 @@
           </button>
           <div class="lock-line"></div>
         </div>
-        
+
         <div class="form-row slider-row">
           <label for="scale-v">Scale V</label>
           <input type="range" id="scale-v" min="0" max="1000" step="1" value="500" />
@@ -153,6 +153,67 @@
         <p class="hint">0° = no masking. Surfaces within this angle of horizontal will not be textured.</p>
       </section>
 
+      <!-- Surface Exclusions -->
+      <section class="panel-section">
+        <h2>Surface Exclusions</h2>
+
+        <!-- Tool buttons -->
+        <div class="excl-tools">
+          <button id="excl-brush-btn" class="excl-tool-btn" title="Brush: paint triangles to exclude" aria-pressed="false">
+            <svg width="13" height="13" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
+              <path d="M3 21c3 0 7-1 7-8V5c0-1.25-.756-2.017-2-2H4c-1.25 0-2 .75-2 1.972V11c0 1.25.75 2 2 2h2c1 0 1 0 1 1v1c0 1-1 2-2 2s-1 .008-1 1.031V20c0 1 0 1 1 1z"/>
+              <path d="M15 21c3 0 7-1 7-8V5c0-1.25-.757-2.017-2-2h-4c-1.25 0-2 .75-2 1.972V11c0 1.25.75 2 2 2h2c1 0 1 0 1 1v1c0 1-1 2-2 2s-1 .008-1 1.031V20c0 1 0 1 1 1z"/>
+            </svg>
+            Brush
+          </button>
+          <button id="excl-bucket-btn" class="excl-tool-btn" title="Bucket fill: flood-fill surface up to a threshold angle" aria-pressed="false">
+            <svg width="13" height="13" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
+              <path d="M19 11V4a2 2 0 0 0-2-2H4a2 2 0 0 0-2 2v13a2 2 0 0 0 2 2h9"/>
+              <path d="M13 17h8m-4-4 4 4-4 4"/>
+            </svg>
+            Fill
+          </button>
+          <button id="excl-erase-toggle" class="excl-tool-btn" title="Toggle: mark or erase mode" aria-pressed="false">
+            <svg width="13" height="13" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
+              <path d="m7 21-4.3-4.3c-1-1-1-2.5 0-3.4l9.6-9.6c1-1 2.5-1 3.4 0l5.6 5.6c1 1 1 2.5 0 3.4L13 21"/>
+              <path d="M22 21H7"/>
+              <path d="m5 11 9 9"/>
+            </svg>
+            Erase
+          </button>
+        </div>
+
+        <!-- Brush type switcher (shown only when Brush is active) -->
+        <div id="excl-brush-type-row" class="form-row hidden">
+          <label>Type</label>
+          <div class="excl-seg">
+            <button id="excl-brush-single" class="excl-seg-btn active">Single</button>
+            <button id="excl-brush-radius-btn" class="excl-seg-btn">Radius</button>
+          </div>
+        </div>
+
+        <!-- Radius slider (shown when Brush + Radius) -->
+        <div id="excl-radius-row" class="form-row slider-row hidden">
+          <label for="excl-brush-radius-slider">Radius</label>
+          <input type="range" id="excl-brush-radius-slider" min="0.1" max="50" step="0.1" value="5" />
+          <input type="number" class="val" id="excl-brush-radius-val" value="5" min="0.1" max="50" step="0.1" />
+        </div>
+
+        <!-- Bucket threshold (shown when Fill is active) -->
+        <div id="excl-threshold-row" class="form-row slider-row hidden">
+          <label for="excl-threshold-slider" title="Maximum dihedral angle between adjacent triangles for the fill to cross">Max angle</label>
+          <input type="range" id="excl-threshold-slider" min="0" max="180" step="1" value="30" />
+          <input type="number" class="val" id="excl-threshold-val" value="30" min="0" max="180" step="1" />
+        </div>
+
+        <!-- Footer: count + clear -->
+        <div class="excl-footer">
+          <span id="excl-count" class="excl-count">0 faces excluded</span>
+          <button id="excl-clear-btn" class="excl-clear-btn">Clear All</button>
+        </div>
+        <p class="hint">Excluded surfaces appear orange and will not receive displacement during export.</p>
+      </section>
+
       <!-- Export -->
       <section class="panel-section">
         <h2>Export</h2>