Add unit API and article unitamount/unitSi patch.

Units use the selected company; article PATCH accepts name/unitamount/unitSi.

docs/api/routes/unit/delete.md

@@ -0,0 +1,33 @@
+# `DELETE /unit`
+
+Protected. Requires a valid session cookie (`credentials: 'include'`).
+
+Delete unit
+
+Deletes `si` for the selected company. Fails with `Unit in use` if articles still reference it.
+
+## Query parameters
+
+| Param | Required | Type | Description |
+|-------|----------|------|-------------|
+| `si` | yes | string |  |
+
+## Response `204`
+
+Deleted
+
+_No content_
+
+## Errors
+
+| Status | Description |
+|--------|-------------|
+| 400 | Missing si or no company selected — `{"error":"…"}` |
+| 401 | Unauthorized — `{"error":"…"}` |
+| 403 | Not authorized — `{"error":"…"}` |
+| 404 | Company or unit not found — `{"error":"…"}` |
+| 409 | Unit in use — `{"error":"…"}` |
+
+---
+
+_Generated from `@openapi` JSDoc. Do not edit by hand — run `npm run docs:api`._