Add customergroup and entity HTTP APIs with address and contact routes.

Expose store-backed CRUD for customer groups, entities, nested addresses, and contacts, matching the documented dashdbschema contracts.

docs/api/routes/entity/create.md

@@ -0,0 +1,48 @@
+# `POST /entity`
+
+Protected. Requires a valid session cookie (`credentials: 'include'`).
+
+Create entity
+
+Creates an entity in a company customer group and writes `entityhistory` (`Erstellt`).
+
+
+## Body (JSON)
+
+```json
+{
+  "customergroupId": 1,
+  "name": "Müller",
+  "firstName": "Anna"
+}
+```
+
+## Response `201`
+
+Created entity
+
+```json
+{
+  "entity": {
+    "id": 1,
+    "customergroupId": 1,
+    "firstName": "…",
+    "name": "…",
+    "createdAt": "2026-08-10T00:00:00.000Z",
+    "updatedAt": "2026-08-10T00:00:00.000Z"
+  }
+}
+```
+
+## Errors
+
+| Status | Description |
+|--------|-------------|
+| 400 | Name required or no company selected — `{"error":"…"}` |
+| 401 | Unauthorized — `{"error":"…"}` |
+| 403 | Not authorized — `{"error":"…"}` |
+| 404 | Company or customer group not found — `{"error":"…"}` |
+
+---
+
+_Generated from `@openapi` JSDoc. Do not edit by hand — run `npm run docs:api`._