XLSX: worksheet drawing text runs ignore theme font inheritance

[developer0hye]

Summary

Worksheet drawing text runs that omit an explicit typeface do not inherit the workbook theme font. Excel renders the three shape labels with the theme's minor Latin sans-serif font, while office2pdf renders them with the Typst serif default.

Found while re-auditing the regression fixture in #434 at 150 DPI against a native Microsoft Excel export.

Reproduction

Convert tests/fixtures/xlsx/theme_color_drawing.xlsx from PR #434 and compare it with a native Excel PDF.

The drawing runs intentionally contain only language and size:

<a:rPr lang="en-US" sz="1100"/>

The workbook theme declares:

<a:minorFont><a:latin typeface="Calibri"/></a:minorFont>

Expected

Drawing labels inherit the applicable DrawingML theme font (Calibri minor Latin in this fixture), or a metric-compatible sans-serif fallback when unavailable.

Actual

accent1, accent1 lighter 60, and accent6 shade 75 render in a serif face. This changes glyph shapes and metrics despite the labels, 11pt size, regular weight, black color, and center alignment otherwise being preserved.

Root-cause evidence

parse_drawing_text_boxes currently reads sz, b, and i from a:rPr, but it neither parses explicit DrawingML typefaces nor resolves omitted typefaces through the workbook theme's font scheme. The resulting TextStyle.font_family is unset.

Visual checklist

• Text content/color/alignment/weight/style: preserved.
• Font family: incorrect.
• Fill colors: correct after XLSX: worksheet-drawing scheme colors ignore the workbook theme #430.
• Shape position/size and page count are tracked separately.
• No underline, hairline, rotation, flip, or clipping is present in this fixture.

Related: #240, #329, #430, #434