fix: add missing translations for sole-trader and search-error strings

[dgjlindsay]

Summary

• Audited every user-facing string in the company-capture component tree (company-capture-component.js, company-search-panel.js, sole-trader.js): mode chips, search aria-label, company-number aria-label, and the sole-trader/search-error messages.
• Three strings had no row in i18n/{nb_NO,nl_NL,sv_SE}.csv: "Select a different sole trader", "Company search is unavailable right now. Please try again shortly.", and "Could not complete sole trader signup. Please try again." Added machine translations matching the neighbouring rows' register/tone; a human pass is expected later.
• es_ES.csv does not exist in this repo (never has, and no test references that locale) — the standing 4-locale ruling doesn't apply to this repo as-is. Flagging for Doug rather than adding a locale with no established convention here.

Why this slipped through CI

This repo has no dev/i18n-audit.sh — the closest thing is Test/Unit/I18n/AdminFormCatalogueTest.php and CompanyGateMessageTranslationTest.php, both PHPUnit. AdminFormCatalogueTest only scans admin-side __() calls (Block/Adminhtml, view/adminhtml/templates, Model/Config/*, admin XML forms) — it never looks at view/frontend/web/js/**. CompanyGateMessageTranslationTest checks two specific hardcoded msgids only. Nothing in CI scans frontend-JS translate() calls at all, so a missing row there renders in English silently, with no test failure.

Test plan

• i18n/*.csv parse cleanly (verified locally: no dup keys, row counts consistent)
• CI green

[claude]

Reviewed: three added CSV rows (nb_NO, nl_NL, sv_SE) match the translate() call sites exactly (company-capture-component.js, company-search-panel.js, sole-trader.js), are alphabetically placed, and introduce no duplicate keys. No critical issues.

Re: the es_ES.csv question raised in the PR description — confirmed the file doesn't exist anywhere in this repo and no test references it, so deferring that to Doug as suggested is reasonable; not a blocker here.

Ready for human approval ✅

[dgjlindsay]

Self-review (clean round): 9 lines added across 3 CSVs, no other rows touched, no duplicate keys introduced, alphabetical placement preserved. All 3 missing msgids ("Select a different sole trader", "Company search is unavailable right now. Please try again shortly.", "Could not complete sole trader signup. Please try again.") verified against the exact translate() call sites in company-capture-component.js / company-search-panel.js / sole-trader.js. Translations checked against neighbouring rows for register/tone (nl_NL formal "u", terminology matching the existing "Sole trader"/"Search for company" rows). CI green (30/30 checks incl. automated code-review). No outstanding findings.

— by Claude