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-architektur.md

@@ -115,7 +115,7 @@ flowchart TD
 - In `pages/**` und `templates/**` sind inline `<script type="module">...</script>` ohne `src` verboten.
 - Seiteninitialisierung liegt in dedizierten ESM-Page-Modulen unter `web/js/pages/*`.
 - Pro Seite wird Konfiguration per `<script type="application/json" id="page-config-<page-key>">...</script>` bereitgestellt und im Modul über `readPageConfig(...)` gelesen.
-- In `pages/**` und `templates/**` muessen alle JS-`src` (eigene und Vendor) ueber `assetVersion('...js...')` laufen.
+- In `pages/**` und `templates/**` müssen alle JS-`src` (eigene und Vendor) über `assetVersion('...js...')` laufen.
 
 ## Mindestchecks vor Merge