fix: add missing GET /projects/{id} endpoint

Frontend workspace was calling GET /projects/{id} which didn't exist,
causing 405 errors and preventing WorkspaceHeader from rendering.

Add get_project endpoint that returns a single project by ID with
ownership verification.

apps/api/src/api/projects.py

@@ -76,6 +76,16 @@ async def list_projects(
     return list(result.scalars().all())
 
 
+@router.get("/{project_id}", response_model=ProjectResponse)
+async def get_project(
+    project_id: uuid.UUID,
+    user_id: uuid.UUID = Depends(get_current_user_id),
+    session: AsyncSession = Depends(get_db_session),
+) -> Project:
+    await _get_user(session, user_id)
+    return await _get_owned_project(project_id, user_id, session)
+
+
 async def _get_owned_project(
     project_id: uuid.UUID,
     user_id: uuid.UUID,