Remove username from Tasks API path when using task IDs

Currently, the **Tasks API** includes the username in the endpoint path. This feels unnecessary because:

* Tasks are already uniquely identified by their **task ID**.
* The frontend has to carry the **owner’s username** around only for this endpoint, which isn’t required anywhere else.
* The original reasoning (ensuring consistency for cases like `@bruno/dev` vs `@kyle/dev`) doesn’t really apply to tasks, since collisions aren’t possible with IDs.

### Proposal

* Drop the **username** from the Tasks API path.
* Rely solely on the **task ID** for identification.