Company matching relied on normText(), which kept legal-form suffixes,
spacing and umlaut spelling — so "Bosch GmbH", "Bosch AG" and "bosch gmbh"
did not match the same entry, making the blacklist unreliable.
Introduce firmaSlug(): transliterate German umlauts, strip diacritics and
trailing legal-form tokens (GmbH/AG/SE/KG/…), then kebab-join. Add a
firma_slug field to jobangebote_blacklist (schema + ALTER/backfill migration)
and match on it for typ firma/firma_stelle/auto, falling back to firma_norm
for legacy rows. POST /joboffers rejects blacklisted offers via matchBlacklist
automatically since offerSignature now carries the slug.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>