docs: restore Chinese design-rationale comments after i18n merge

PR #1 condensed the existing Chinese comments into shorter English,
dropping the 'why / don't revert to X' notes the project relies on
(merged-mesh face lookup, Identity-not-null transforms, background
section clip, ...). Restore the original comments verbatim where the
code is unchanged; new i18n code keeps its English comments. Two
FacesContent/MergedContent notes are corrected to the current render
modes. Comment-only change (verified: comment-stripped code identical).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/SmokeTest/TreeDump.cs

@@ -1,4 +1,4 @@
-// Print the STEP object hierarchy after import with HierarchyToBlocks enabled.
+// 實驗工具：印出 STEP 匯入後的物件階層（HierarchyToBlocks=true）
 using CADability;
 using CADability.GeoObject;