docs: replace ASCII umlaut fallbacks with proper äöüß across all .md

Most German docs were written with `ue`/`ae`/`oe`/`ss` ASCII fallbacks
(`fuer`, `aenderung`, `koennen`, `gemaess`) — relic from older toolchain
constraints. Replaced 237 occurrences across 38 .md files with proper
umlauts and ß so the docs read naturally.

Substitutions are constrained to plain prose: fenced code blocks
(```...```), inline code spans (`...`), markdown link targets `[..](..)`,
and HTML comments are preserved verbatim. Path references like
`docs/howto-erste-aenderung.md` keep their original (umlaut-replaced)
filenames — only the surrounding prose is normalised.

Tool: bin/fix-md-umlauts.py (idempotent — no-op on already-clean files).
Re-runnable if ASCII fallbacks creep back in via copy-paste.

Doc-link-check + doc-drift-check stay green.

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

docs/explanation-di-container.md

@@ -103,6 +103,6 @@ $meinService = app(\MintyPHP\Service\MeinNeuerService::class);
   den konkreten Service direkt registrieren und per `app()` holen.
 - Der Container lebt **pro HTTP-Anfrage** — er wird in `web/index.php` initialisiert
   und über `setAppContainer()` im globalen State abgelegt.
-- In CLI-Commands wird der Container separat initialisiert (ueber die Runtime-Bootstrap-Klassen unter `core/Console/Support/`).
+- In CLI-Commands wird der Container separat initialisiert (über die Runtime-Bootstrap-Klassen unter `core/Console/Support/`).
 - In `core/Service/**` außerhalb von `*Factory.php` niemals `new ...Factory()`,
   `new ...Service()` oder `new ...Repository()` direkt instanziieren.