test(goldens): regenerate country-field state goldens for the neutral hint (#825)

[TaprootFreak]

Problem

staging Visual Regression is red: #825 ("neutralize the misleading hint") changed the country-field countryHint from "Schweiz"/"Switzerland" to "Land auswählen"/"Select country" and regenerated the default country goldens, but the state goldens added by #828 (nationality) and #829 (registration wizard) — which render the empty country field with the old hint — were merged around the same time and were not regenerated for #825's change. On current staging they still show "Schweiz", so they no longer match the rendered UI.

Fix

Regenerated exactly the 11 stale state goldens against current staging (with #825's new hint). No test/lib code changed — only the PNG baselines:

• kyc_nationality_page_{submit_loading, submit_failure, validation_error}
• kyc_registration_page_{address_step, tax_step, forwarding_failed_snackbar, submit_failure_snackbar}
• kyc_registration_personal_step_{account_type_open, phone_prefix_open, validation_error}
• kyc_registration_address_step_validation_error

Each now renders the neutral "Land auswählen" placeholder. The other state goldens in those files (dropdown-open, country-loading, country-error) don't show the hint and are unchanged.

Verification

Regenerated on the CI-identical toolchain (Flutter 3.41.6), two --update-goldens runs byte-identical; git diff shows exactly these 11 PNGs and nothing else; flutter analyze clean; the four affected golden test files pass against the new baselines. This restores staging to green.