Rolls up PR #554 (locale-prefix follow-ups — login regression fix,
sitemap source dedup, redirect_invalid_locale swap-vs-strip, 22 new
tests), PR #555 (language switcher country-qualifier dedup), and the
etcher 0.3 → 0.4 / fresco 0.5.2 → 0.5.3 bumps.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>