A minimal JSON store — store and retrieve JSON blobs by ID.
| POST | /b | Create a bin. Optional X-Bin-Name header sets the name. |
| GET | /b | List all bins. |
| GET | /b/:id | Read a bin. Add ?version=N for a specific version. |
| PUT | /b/:id | Update a bin. Optional X-Bin-Name header renames it. |
| GET | /b/:id/versions | List all versions of a bin. |
| DELETE | /b/:id | Delete a bin. |