[Clippy] feat(html): render DOCX text boxes as inline-block divs in WmlToHtmlConverter

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Closes #65

Summary

Text boxes in DOCX (w:drawing containing wps:wsp/wps:txbx) were silently dropped by WmlToHtmlConverter. The converter's ProcessDrawing method returned null for any drawing that wasn't an image (no a:blipFill), so all text box content was lost in HTML output.

Root Cause

ProcessDrawing only handled the image path (Pic.blipFill). There was no code path for wps:wsp / wps:txbx shapes that contain text content.

Fix

Added ProcessTextBoxDrawing called from ConvertToHtmlTransform before the existing ProcessImage call:

1. Detection: checks a:graphicData/wps:wsp/wps:txbx in both wp:anchor (floating) and wp:inline containers.
2. Content extraction: walks w:txbxContent paragraphs through the existing recursive HTML transform pipeline — all paragraph formatting, runs, hyperlinks, nested tables, etc. are handled correctly.
3. Sizing: uses wp:extent cx/cy (in EMUs) to set width and min-height CSS properties.
4. Float: wp:anchor (floating) text boxes get float: left so surrounding body text flows around them.

Emitted HTML

(div style="display: inline-block; float: left; min-height: 1.00in; overflow: hidden; padding: 2pt; width: 2.00in;")
  <p>...text box content rendered through normal paragraph pipeline...</p>
(/div)
```

## Trade-offs / Limitations

- **Absolute positioning** is not implemented — anchored text boxes use `float: left` rather than `position: absolute` with computed coordinates. This is intentional: computing exact pixel offsets requires knowledge of the container's layout dimensions, which the converter doesn't track. The float approach preserves text flow without data loss.
- **Inline text boxes** (`wp:inline`) get `display: inline-block` without float, which is typically correct for inline shapes.
- **No border/fill styling** from `wps:spPr` shape properties — the div has no border by default (shape fill and outline are ignored). This keeps the implementation minimal.

## Test Added

`HC063_TextBoxRenderedAsDiv` — creates a minimal DOCX with a floating text box programmatically and verifies:
- Text box content appears in the HTML output (not dropped)
- A `div` with `display: inline-block` is present
- The div has `width:`, `min-height:`, and `float: left` from the drawing extent

## Test Status

```
Test run summary: Passed!
  total: 1208
  failed: 0
  succeeded: 1207
  skipped: 1 (pre-existing)
  duration: 1m 22s

✅ All 1207 tests pass. dotnet csharpier check . passes.

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