feat: add delete functionality for exercises and routines

src/ASTRAIN.Api/Endpoints/RoutineEndpoints.cs

@@ -160,6 +160,23 @@ internal static class RoutineEndpoints
             .WithSummary("Update routine")
             .WithDescription("Updates routine metadata and exercise ordering.");
 
+        group.MapDelete("/users/{userId}/routines/{routineId:int}", async (string userId, int routineId, AppDbContext db) =>
+            {
+                var user = await UserProvisioning.EnsureUserAsync(db, userId);
+                var routine = await db.Routines.FirstOrDefaultAsync(r => r.Id == routineId && r.UserId == user.Id);
+                if (routine is null)
+                {
+                    return Results.NotFound();
+                }
+
+                db.Routines.Remove(routine);
+                await db.SaveChangesAsync();
+
+                return Results.NoContent();
+            })
+            .WithSummary("Delete routine")
+            .WithDescription("Deletes a routine and its associated data for the specified user.");
+
         return group;
     }
 }