[feature]: Add project member management (POST/PATCH/DELETE) to REST API v1

Is there an existing issue for this?

• I have searched the existing issues

Summary

The current REST API v1 only exposes GET /api/v1/workspaces/{slug}/projects/{project_id}/members/ for reading project members. There is no endpoint to add, update, or remove project members via the API. These operations work fine through the web UI (which uses internal session-based endpoints), but are not available to API key / Personal Access Token consumers. This makes it impossible to automate member management across projects.

Requested endpoints

POST /api/v1/workspaces/{slug}/projects/{project_id}/members/
PATCH /api/v1/workspaces/{slug}/projects/{project_id}/members/{member_id}/
DELETE /api/v1/workspaces/{slug}/projects/{project_id}/members/{member_id}/

Why should this be worked on?

Teams managing many projects need to automate member assignments. For example, when onboarding a new team member, a workspace admin should be able to programmatically add them to all (or a subset of) projects via a script or integration, rather than manually clicking through each project in the UI. This is especially painful for workspaces with 30+ projects.

Currently, even a workspace admin with a Personal Access Token gets a 403 Forbidden when POSTing to the members endpoint. The web UI can do it, so the backend logic already exists — it just needs to be exposed through the public API.