feat(docs): mkdocs-style documentation site served at /docs

Full documentation hub replacing the release-notes-only view:
- Handbook pages (docs/handbook) for all features and admin/betrieb
- API reference generated from lib/api-spec/openapi.yaml via
  scripts/src/generate-docs.mjs (replaces sync-release-docs.mjs):
  endpoints, schemas/fields, search index, per-release snapshots
- mkdocs layout: sidebar nav, right TOC with scrollspy, search overlay,
  version dropdown, repo link
- FieldHelp (?) buttons in forms linking to reference field docs
- v0.7.0 release notes backfilled, v0.8.0 release notes added

artifacts/toolrate/src/i18n/locales/de.json

@@ -183,10 +183,22 @@
     "backHome": "Zurück zur Startseite"
   },
   "docs": {
-    "title": "Versionsdokumentation",
-    "subtitle": "Version-gebundene Dokumentation je Release — was ist neu, was hat sich geändert und was beim Upgrade zu beachten ist.",
+    "title": "Dokumentation",
+    "subtitle": "Version-gebundene Dokumentation — Release-Notes, Endpunkte und Datenfelder je Version.",
     "backToIndex": "Alle Releases",
-    "noDocs": "Noch keine Release-Dokumentation verfügbar."
+    "noDocs": "Keine Dokumentation für diesen Pfad verfügbar.",
+    "version": "Version",
+    "latest": "Aktuell",
+    "repo": "Repository",
+    "nav": "Dokumentation",
+    "guides": "Handbuch",
+    "endpoints": "Endpunkte",
+    "schemas": "Datenmodelle",
+    "releases": "Release-Notes",
+    "reference": "API-Referenz",
+    "referenceIntro": "Automatisch aus der OpenAPI-Spezifikation generiert — alle Endpunkte und Datenfelder der aktuellen Version.",
+    "onThisPage": "Auf dieser Seite",
+    "searchPlaceholder": "Doku durchsuchen…"
   },
   "command": {
     "navigate": "Navigation",