fix(form_fit): lay bold glyphs in the 한양 faces out a twentieth of the em wider

[airmang]

Summary

• FormFit and the page estimate laid a bold glyph out at its regular advance in every face.
• Hancom Office draws bold glyphs in the 한양 faces (한양신명조, 한양중고딕, 한양견고딕) a twentieth of the em wider. It adds that before it rounds the advance to whole layout units, so "가" at 14 pt is 1472 HWPUNIT, not 1400.
• Bold glyphs in the other faces keep their regular advances, as before.
• TextStyle gains bold, read from the character shape's hh:bold. The wider advance applies at 장평 100 % only.

Test plan

• A Hancom-saved fixture (formfit_bold_advances, 한양신명조 regular and bold at 9 to 20 pt, three glyphs then a tab): every tab width matches. This test and the advance test fail before the change.
• Lint, format, type checks and the other repository gates
• Layout and FormFit tests; full test suite: no new failures

🤖 Generated with Claude Code

[airmang]

Reviewed exact head 48c4ac7. TextStyle.bold is appended with a False default, preserving existing positional arguments; reference parsing carries bold through both property paths. Inspected glyph-face selection, emoji/space exclusions, rounding and cache keys. Hanyang widening is explicitly limited to the measured ratio-100 path; other faces retain prior advances. Direct width assertions and Hancom-saved tab fixtures cover the change. No unresolved findings.

All 13 exact-head CI checks pass; verified workflow head SHA and read test/lint/type/hygiene logs (6,868 passed, 18 skipped, 1 xfailed). Locally, 147 FormFit tests pass at the PR head. After #499 merged, integrated current main 038ad54 without conflicts and ran 262 related FormFit/layout regression tests: all passed. Tested tree 27803fe11d269579ecb87eec1fcf5d9332fa42e5. Ready for a SHA-guarded squash merge; COMMENT because this account owns the PR.