feat(docs): version-bound release documentation served at /docs

Adds a docs pipeline so each release has a version-bound Markdown
document (docs/releases/vX.Y.Z.md) rendered publicly in the app:

- sync-release-docs.mjs copies docs/releases/*.md into the toolrate
  public dir and generates index.json before every dev/build
- /docs lists all releases; /docs/:version renders the sanitized
  Markdown (marked + DOMPurify, typography styles)
- template + workflow documented in docs/README.md
- current release (v0.6.0) documented as the first entry

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

@@ -12,6 +12,7 @@
     "trash": "Papierkorb",
     "admin": "Admin",
     "redundancy": "Redundanz",
+    "docs": "Doku",
     "search": "Tools suchen…"
   },
   "auth": {
@@ -181,6 +182,12 @@
     "text": "Diese Seite existiert nicht.",
     "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.",
+    "backToIndex": "Alle Releases",
+    "noDocs": "Noch keine Release-Dokumentation verfügbar."
+  },
   "command": {
     "navigate": "Navigation",
     "recent": "Zuletzt besucht",