fix(form_fit): give a no-break space its 장평 and no 자간

[airmang]

Summary

• FormFit and the page estimate laid a no-break space (hp:nbSpace) out like a space: its 장평 and its 자간 both applied.
• Hancom Office applies the 장평 to a no-break space but not the 자간. At 9 pt, 장평 120 % and 자간 -12 %, one is 536 HWPUNIT, not 472.
• Spaces and fixed-width spaces keep their advances, as before.

Test plan

• A Hancom-saved fixture (formfit_space_scaling, 맑은 고딕 at 9, 10 and 14 pt under eight 장평 and 자간): "가", three no-break spaces, fixed-width spaces or spaces, then a tab. Every tab width matches. The test fails before the change.
• Lint, format, type checks and the other repository gates
• Layout and FormFit tests

🤖 Generated with Claude Code

[airmang]

Reviewed exact head 5decc87 and surrounding space/glyph scaling paths. The hp:nbSpace mapping takes width ratio while excluding letter spacing in the half-em path; ordinary/fixed-width space handling is preserved. Checked direct 536-vs-472 assertions and Hancom-saved tab fixtures across sizes and scaling combinations. No code defect found. All 146 local FormFit tests pass. All 13 exact-head checks pass; verified workflow SHA and read test/lint/type/hygiene logs (6,867 passed, 18 skipped, 1 xfailed).

Merge is held: scratch integration with current main 97c2bef reproduces content conflicts in CHANGELOG.md, src/hwpx/form_fit/measure.py, and tests/test_form_fit_hancom_rules.py after #501. Resolve preserving both bold-width and no-break-space behavior and both fixture/test additions, then rerun the combined FormFit/layout regression tests and latest-head checks. No resolution was pushed; conflicted integration was aborted.