perf(web): speed up folder menu sorting

[AksharP5]

What Changed

Folder breadcrumb menus repeat locale setup for each filename comparison. Reuse one lazily created collator per menu calculation, keeping the existing natural ordering and folder precedence.

Fixes #10191.

Why

On this repository's 169-entry apps/web/src folder, the complete menu-list helper dropped from 1.39 ms to 0.20 ms. This is a warmed Node 26.8.1 benchmark on Linux, not measured UI latency. The output was identical.

Verification

• All 10 filePath.test.ts tests pass, including natural ordering and stable ties across case and leading-zero variants.
• Scoped TypeScript check, targeted lint, formatting, and git diff --check pass.
• Independent code review found no issues.

Checklist

• This PR is small and focused
• I explained what changed and why

No visual or interaction changes.

Implemented and reviewed with GPT-6 through Codex.

[macroscopeapp]

Approvability

Verdict: Approved at 9fce8b0

Macroscope's review found this PR approvable — This small optimization reuses a lazily created collator while preserving the existing folder precedence and natural filename ordering. The accompanying test covers equivalent-name ordering, and no broader runtime capability or configuration behavior is introduced.

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