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/en.json

@@ -183,10 +183,22 @@
     "backHome": "Back to Home"
   },
   "docs": {
-    "title": "Release Documentation",
-    "subtitle": "Version-bound documentation for each release — what's new, what changed, and what to know when upgrading.",
+    "title": "Documentation",
+    "subtitle": "Version-bound documentation — release notes, endpoints and data fields per version.",
     "backToIndex": "All releases",
-    "noDocs": "No release documentation available yet."
+    "noDocs": "No documentation available for this path.",
+    "version": "Version",
+    "latest": "Latest",
+    "repo": "Repository",
+    "nav": "Documentation",
+    "guides": "Guide",
+    "endpoints": "Endpoints",
+    "schemas": "Data models",
+    "releases": "Release notes",
+    "reference": "API reference",
+    "referenceIntro": "Generated automatically from the OpenAPI spec — all endpoints and data fields of the current version.",
+    "onThisPage": "On this page",
+    "searchPlaceholder": "Search docs…"
   },
   "command": {
     "navigate": "Navigate",