fix(UC-02): LOW review items — anchored path strip + corner offset doc

- Use substring instead of replace for path cleanup (anchored, no double-strip risk)
- Document that corner_decorations ignores x/z offsets (by design)

src/main/java/com/tiedup/remake/worldgen/HangingCagePiece.java

@@ -637,6 +637,8 @@ public class HangingCagePiece extends StructurePiece {
         int[][] corners = layout.innerCorners();
 
         // Corner decorations (e.g. cobwebs low+high, soul fire, snow layers)
+        // Note: only y_offset is used here — x/z offsets are ignored because corners
+        // are placed at all 4 inner corners and direction logic would differ per corner.
         for (DecorationConfig.PositionedBlock pb : deco.cornerDecorations()) {
             for (int[] c : corners) {
                 if (layout.isInShape(c[0], c[1]) && !layout.isWall(c[0], c[1])) {