fix(07): UAT fixes — SMTP test email, DKV routing, Exchange domain field

- SMTP: add test-to field, send real email via sendMail() instead of verify()
- SMTP: fix no_auth warning shown as error for open-relay servers
- DKV: register dkv-fleet in MODULE_REGISTRY (fixes "Modul nicht gefunden")
- DKV: add dynamic [category]/[moduleSlug]/settings + vehicles sub-routes
- DKV: settings/vehicles links use useParams for consistent URLs
- DKV: add gear icon settings link to module main page
- DKV: rename module to "DKV-Rechnung" in seed + translations
- DKV: add optional domain field for Exchange (WebCredentials 3rd arg)
- DKV: hide IMAP-only fields (Port/Verschlüsselung/Ordner) when Exchange selected
- DKV: hide Exchange-only field (Domain) when IMAP selected
- Prisma: add domain column to DkvModuleConfig

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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