feat(ooxml): Preserve VML comment styling during round-trips

[arcaputo3]

Background

When modifying a sheet that contains comments, the VML drawing file (xl/drawings/vmlDrawingN.vml) is regenerated from scratch rather than preserved from the source file. This means custom VML styling is lost.

Related: #166 (fix for comments overwrite bug)

What VML Controls

VML (Vector Markup Language) stores visual properties for comment boxes:

• Position (margin-left, margin-top)
• Size (width, height)
• Fill color (custom colors beyond default yellow)
• Stroke/border settings
• Shadow settings
• Visibility state (always visible vs hover-only)
• z-index ordering
• Custom anchor offsets

Current Behavior

Scenario	VML Behavior
Unmodified sheet	✅ Preserved byte-for-byte
Modified sheet	❌ Regenerated with defaults

When regenerated, comments get fixed defaults:

• Size: 108pt × 59.25pt
• Color: infoBackground [80] (yellow)
• Position: Calculated from cell position
• Visibility: Hidden (shows on hover)

Proposed Solution

1. Parse VML on read - Extract comment visual properties into domain model
2. Extend Comment type - Add optional CommentStyle or VmlProperties field
3. Preserve on write - Use stored properties when regenerating VML

Complexity

VML is a complex legacy format. This is a non-trivial enhancement that requires:

• VML parser (currently binary passthrough)
• Domain model extension
• Round-trip testing for VML properties

Acceptance Criteria

• Comments with custom sizes preserve size on round-trip
• Comments with custom positions preserve position on round-trip
• Comments with custom colors preserve color on round-trip
• Comments with "always visible" state preserve visibility
• Existing tests continue to pass

Priority

Low - This is a fidelity enhancement, not a correctness issue. Comments content and author are preserved correctly; only visual styling is affected.

[arcaputo3]

Closing — VML comment styling is now preserved during round-trips via VmlDrawing.scala. VML drawings are read and re-serialized faithfully.