Simplify rich-inline: unify stepRichInlineLine/Stats and remove containsCJKText wrapper

[shaun0927]

Summary

Two small simplification opportunities in the v0.0.5 code, both pure refactors with no behavior change.

1. stepRichInlineLine and stepRichInlineLineStats share ~180 lines of near-identical logic

rich-inline.ts:211–387 and rich-inline.ts:389–519 implement the same line-stepping loop. The only difference is whether a collectFragment callback fires. Since stepRichInlineLine already accepts an optional collectFragment parameter, the stats variant could be replaced with stepRichInlineLine(flow, maxWidth, cursor, undefined).

Evidence of drift risk: PR #132 had to apply the same overflow guard to both functions in parallel — the exact duplication pattern that makes one-sided patches easy to miss.

I verified the two functions produce identical lineCount and maxLineWidth across multiple item/width combinations (simple text, CJK multi-item, atomic chips with extraWidth, mixed items), so unification would not change behavior.

2. containsCJKText() is a single-call-site passthrough to isCJK()

// analysis.ts:161–163
function containsCJKText(text: string): boolean {
  return isCJK(text)
}

One call site at line 1214. Similar to the isCJK dedup and no-op removal in PR #118.

Motivation

Both align with the repo's holistic-pass simplification principle. Neither changes behavior — the first reduces the surface for future one-sided patches in rich-inline, and the second removes a trivial indirection.

Happy to submit a PR if these look reasonable.

[shaun0927]

Submitted PR #138 for this.