Refactor surface masking and exclusion features

- Renamed "Surface Mask" section to "Mask Angles" for clarity in index.html.
- Updated translation keys and tooltips to reflect the new terminology in i18n.js.
- Removed the erase toggle button from the exclusion panel and implemented Shift key functionality to toggle erase mode in main.js.
- Adjusted brush radius handling to improve user experience and updated related UI elements in index.html.
- Enhanced the subdivision process to track original face IDs for better masking accuracy in subdivision.js.
- Added CSS styles for new UI elements and improved layout in style.css.

index.html

@@ -213,9 +213,9 @@
         </div>
       </section>
 
-      <!-- Surface Mask -->
+      <!-- Mask Angles -->
       <section class="panel-section">
-        <h2 data-i18n="sections.surfaceMask" data-i18n-title="tooltips.surfaceMask" title="0° = no masking. Surfaces within this angle of horizontal will not be textured.">Surface Mask ⓘ</h2>
+        <h2 data-i18n="sections.maskAngles" data-i18n-title="tooltips.maskAngles" title="0° = no masking. Surfaces within this angle of horizontal will not be textured.">Mask Angles ⓘ</h2>
         <div class="form-row slider-row">
           <label for="bottom-angle-limit" data-i18n="labels.bottomFaces" data-i18n-title="tooltips.bottomFaces" title="Suppress texture on downward-facing surfaces within this angle of horizontal">Bottom faces</label>
           <input type="range" id="bottom-angle-limit" min="0" max="90" step="1" value="5" />
@@ -230,7 +230,7 @@
 
       <!-- Surface Exclusions -->
       <section class="panel-section">
-        <h2 id="excl-section-heading" data-i18n="sections.surfaceExclusions" data-i18n-title="tooltips.surfaceExclusions" title="Excluded surfaces appear orange and will not receive displacement during export.">Surface Exclusions ⓘ</h2>
+        <h2 id="excl-section-heading" data-i18n="sections.surfaceMasking" data-i18n-title="tooltips.surfaceMasking" title="Mask surfaces to control which areas receive displacement.">Surface Masking ⓘ</h2>
         <p id="excl-hint" class="excl-hint" style="display:none"></p>
 
         <!-- Mode toggle: Exclude / Include Only -->
@@ -265,16 +265,6 @@
             </svg>
             <span data-i18n="excl.toolFill">Fill</span>
           </button>
-          <button id="excl-erase-toggle" class="excl-tool-btn" aria-pressed="false"
-            data-i18n-title="excl.toolEraseTitle"
-            title="Toggle: mark or erase mode">
-            <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>
-            <span data-i18n="excl.toolErase">Erase</span>
-          </button>
         </div>
 
         <!-- Brush type switcher (shown only when Brush is active) -->
@@ -282,15 +272,15 @@
           <label data-i18n="labels.type">Type</label>
           <div class="excl-seg">
             <button id="excl-brush-single" class="excl-seg-btn active" data-i18n="brushType.single">Single</button>
-            <button id="excl-brush-radius-btn" class="excl-seg-btn" data-i18n="brushType.radius">Radius</button>
+            <button id="excl-brush-radius-btn" class="excl-seg-btn" data-i18n="brushType.circle">Circle</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" data-i18n="labels.radius">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" />
+          <label for="excl-brush-radius-slider" data-i18n="labels.size">Size</label>
+          <input type="range" id="excl-brush-radius-slider" min="0.2" max="100" step="0.2" value="10" />
+          <input type="number" class="val" id="excl-brush-radius-val" value="10" min="0.2" max="100" step="0.2" />
         </div>
 
         <!-- Bucket threshold (shown when Fill is active) -->
@@ -302,7 +292,8 @@
 
         <!-- Footer: count + clear -->
         <div class="excl-footer">
-          <span id="excl-count" class="excl-count">0 faces excluded</span>
+          <span id="excl-count" class="excl-count">0 faces masked</span>
+          <span id="excl-shift-hint" class="excl-shift-hint" data-i18n="excl.shiftHint">Hold Shift to erase</span>
           <button id="excl-clear-btn" class="excl-clear-btn" data-i18n="ui.clearAll">Clear All</button>
         </div>
       </section>