Add clay pieces, masking, and topology editing to sculpt

Add pastel presets, piece selection and colors, mask brushes, subdivision and conservative decimation with bounded worker operations and mixed undo history.

Amp-Thread-ID: https://ampcode.com/threads/T-01a0b4b4-202c-73f1-984d-9a55c88f9c83
Co-authored-by: Heaust Azure <heaust.azure@gmail.com>

server/web/assets/sculpt/styles.css

@@ -197,6 +197,79 @@ summary {
   width: min(264px, calc(100vw - 74px));
   border-radius: 6px;
 }
+.pieces-panel {
+  left: max(58px, calc(env(safe-area-inset-left) + 50px));
+  width: min(248px, calc(100vw - 74px));
+  border-radius: 6px;
+}
+.pieces-panel .btn {
+  background: #262a30;
+  color: #d4d7db;
+}
+.pieces-panel .btn:hover {
+  background: #343b45;
+}
+#piece-list {
+  display: grid;
+  gap: 3px;
+  max-height: 180px;
+  overflow-y: auto;
+}
+.piece-row.btn {
+  justify-content: flex-start;
+  gap: 8px;
+}
+.pieces-panel .piece-row[aria-pressed="true"] {
+  background: #386fa9;
+  color: white;
+}
+.piece-row i {
+  width: 14px;
+  height: 14px;
+  border-radius: 50%;
+  flex-shrink: 0;
+}
+.piece-material {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  margin: 10px 0;
+  font-size: 12px;
+}
+.piece-material .btn {
+  margin-left: auto;
+}
+#piece-color {
+  width: 30px;
+  height: 26px;
+  padding: 0;
+  border: 0;
+  background: transparent;
+  cursor: pointer;
+}
+.preset-grid {
+  display: grid;
+  grid-template-columns: repeat(5, 1fr);
+  gap: 3px;
+  margin-block: 10px;
+}
+.preset-grid .btn {
+  padding: 5px;
+  height: 36px;
+}
+.preset-grid svg {
+  width: 23px;
+  height: 23px;
+  fill: none;
+  stroke: currentColor;
+  stroke-width: 1.4;
+}
+.piece-actions {
+  display: grid;
+  grid-template-columns: 1fr 1fr;
+  gap: 5px;
+  padding-top: 8px;
+}
 .panel-heading {
   display: flex;
   align-items: center;