feat: clear feedback form after submission (closes #4026)

src/ui/FeedbackWindow.swift

@@ -88,6 +88,8 @@ class FeedbackWindow: NSWindow {
                 Logger.error("HTTP call failed:", response ?? "nil", error ?? "nil")
             }
         }).resume()
+        issueTitle.stringValue = ""
+        body.stringValue = ""
         close()
     }