fix: currency symbols stick to adjacent numbers during line breaking

[ImpulseB23]

Fixes #98

Currency symbols ($, £, €, ¥, etc.) were getting segmented separately from adjacent text by Intl.Segmenter, leaving a breakable gap. So pretext could wrap between $ and 500, or between 500 and €, which browsers don't do.

Added a \p{Sc} (Unicode currency symbol category) check to both the forward-sticky and left-sticky merge passes in analysis.ts. This covers prefix ($500) and postfix (500€) currencies, matching browser behavior.

Before:

• $500 -> segments ["$", "500"] (breakable)
• 500€ -> segments ["500", "€"] (breakable)

After:

• $500 -> segments ["$500"]
• 500€ -> segments ["500€"]

Tested in Chromium on Windows across $, £, €, ¥, ₹ at various widths. All match browser line counts. 81/81 existing tests pass.

[Copilot]

Pull request overview

Fixes incorrect line-break opportunities introduced by Intl.Segmenter splitting currency symbols away from adjacent text, bringing Pretext wrapping behavior in line with browser layout.

Changes:

• Add a Unicode currency-symbol (\p{Sc}) detector in analysis.ts.
• Treat currency symbols as both left-sticky and forward-sticky merge candidates so $500 / 500€ are kept as single segments.

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