Validate screenshot URLs server- and client-side

Endpoints/SuggestEndpoints.cs

@@ -51,6 +51,11 @@ public static class SuggestEndpoints
                 return Results.BadRequest(new { error = "Name is required and must be <= 100 characters." });
             }
 
+            if (!EndpointHelpers.IsValidImageUrl(request.ScreenshotUrl))
+            {
+                return Results.BadRequest(new { error = "Screenshot URL must be http(s) and end with an image file extension." });
+            }
+
             var player = await EndpointHelpers.GetAuthenticatedPlayer(ctx, db);
             if (player is null) return Results.Unauthorized();
 
@@ -118,6 +123,11 @@ public static class SuggestEndpoints
                 return Results.BadRequest(new { error = "Name is required and must be <= 100 characters." });
             }
 
+            if (!EndpointHelpers.IsValidImageUrl(request.ScreenshotUrl))
+            {
+                return Results.BadRequest(new { error = "Screenshot URL must be http(s) and end with an image file extension." });
+            }
+
             var suggestion = await db.Suggestions.FirstOrDefaultAsync(s => s.Id == id);
             if (suggestion == null) return Results.NotFound(new { error = "Suggestion not found." });