fix(xlsx): fill table cells to the full line height with Excel insets

[developer0hye]

Summary

XLSX auto-height rows rendered ~22% taller than Excel — 17.15pt vs 14.0pt for a 10pt font (issue #396). Two causes:

1. Single-line cells occupied only the metric box. A cell line used the font's ascender+descender (~0.94em); the single-spacing leading tops up the space between lines, so a one-line cell was left short and, with the default inset, the auto row overflowed. Cells now emit a fixed line box spanning the font's full hhea line (split by the ascender/descender ratio, zero leading) — the height Word gives a cell line. This also lifts DOCX Korean cells toward Word (18pt → 21pt; the residual to Malgun's own metrics is DOCX: table-cell rows render about 4.3pt shorter than Word #404).
2. Typst's default 5pt vertical cell inset overflowed the row. XLSX tables now use ~1pt vertical / 2pt horizontal insets (the horizontal value the column-spill estimate already assumes).

Measured on 06_sales_dashboard_en.xlsx: row pitch drops from 17.15pt to 13.5pt against Excel's 14.0pt (0.5pt residual, no content clipped).

Related issue

Fixes #396

Testing

• cargo test --workspace — green
• Local bulk regression gate — PASS (shared cell-paragraph line-height path; the gate covers every DOCX/XLSX table fixture)
• Updated the two table-cell line-height tests to the full-hhea-box contract
• Converted 06_sales_dashboard_en.xlsx (rows match Excel) and 03_meeting_minutes_ko.docx (Korean cells taller, toward GT, no clipping)

Visual impact

• No rendered PDF change
• Rendered PDF change or visual evidence added
• Reason:

Visual audit

• Issue: XLSX: auto-height rows render ~22% taller than Excel #396
• Fixture: 06_sales_dashboard_en.xlsx (synthetic real-world audit set, external)
• Page(s): 1
• Renderer and DPI: pdftoppm, 150 DPI
• Evidence mode: fix
• New follow-up issues found in this audit: None
• GT: assets/bugfixes/issue-396/gt.jpg
• Before: assets/bugfixes/issue-396/before.jpg
• After: assets/bugfixes/issue-396/after.jpg

Visual comparison

GT	Before	After

Required inspection

• Rendered all evidence at 150 DPI or higher
• Stored progressive JPEG quality 86 assets with metadata stripped
• Inspected matched region crops at full resolution
• Ran the 5% fuzz pixel-difference sweep
• Inventoried hairlines and border dash styles
• Inventoried font weight, italic, and underline emphasis

Deviation audit

Check	Result
Page count/order	Matches GT
Element presence	Matches GT
Position/size	Fixed (row pitch 13.5pt vs Excel 14.0pt, was 17.15pt)
Rotation/flip	No deviation observed
Fill	Matches GT (color-scale cells, data bars)
Stroke/border	Matches GT
Text content	Matches GT
Font family/weight/style	Matches GT
Text color	Matches GT
Alignment	Matches GT
Line/paragraph spacing	Fixed (cells fill the full line box)
Clipping/overflow	Matches GT (no cell content clipped)

Checklist

• Commits include a Signed-off-by line
• PR scope contains one root cause
• Remaining visual deviations each reference an open issue

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