chore(markdown): Restructure backend docs

markdown/dev/reference/backend/rbac/en.md

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+---
+title: Access control
+---
+
+The backend API implements role-based access control (RBAC). Each
+user has a role and that role determines what they can and cannot do.
+
+## Roles vs levels
+
+In practice, the different user roles map to a permission level between
+`0` and `8`.
+The available roles and their privilege levels are:
+
+- **user**: `4`
+- **bughunter**: `5`
+- **support**: `6`
+- **admin**: `8`
+
+We offer more fine-grained control over the permission level when
+authenticating with API keys.  When you create an API key, you can choose any
+permissioning level that is equal or lower than your own role's permission level.
+
+This allows you to -- for example -- generate an API key that only have read
+access to your data.
+
+## Permission levels
+
+The table below lists the privilege of all levels as well as their
+corresponding <small><small><b>`role`</b></small></small>
+
+| Level  | Abilities | <small><small>`user`</small></small> | <small><small>`bughunter`</small></small> | <small><small>`support`</small></small> | <small><small>`admin`</small></small> |
+| --: | -- | :--: | :--: | :--: | :--: |
+| `0`    | authenticate                                     | ✅ | ✅ | ✅ | ✅ |
+| `1`    | **read** people and patterns                     | ✅ | ✅ | ✅ | ✅ |
+| `2`    | **read all** account data                        | ✅ | ✅ | ✅ | ✅ |
+| `3`    | **write** people or patterns                     | ✅ | ✅ | ✅ | ✅ |
+| `4`    | **write all** account data                       | ✅ | ✅ | ✅ | ✅ |
+| `5`    | **read** people or patterns of **other users**   | ❌ | ✅ | ✅ | ✅ | 
+| `6`    | **read all** account data of **other users**     | ❌ | ❌ | ✅ | ✅ | 
+| `7`    | **write** account data of **other users** through **specific support methods** | ❌ | ❌ | ✅ | ✅ | 
+| `8`    | impersonate other users, **full write access**   | ❌ | ❌ | ❌ | ✅ |
+