fix(clipboard): route copy actions through Electron

Replace renderer clipboard calls with the validated main-process IPC writer for link names, URLs, package batches, backup keys, diagnostics, error details, and masked account identifiers. Raise the validated payload limit to one MiB so complete link packages copy without truncation while preserving empty and oversized input rejection.

tests/clipboard-write.test.ts

@@ -0,0 +1,15 @@
+import { describe, expect, it } from "vitest";
+import { CLIPBOARD_WRITE_MAX_BYTES, validateClipboardWriteText } from "../src/main/clipboard-write";
+
+describe("clipboard write validation", () => {
+  it("accepts complete large link packages up to one MiB", () => {
+    const text = "x".repeat(CLIPBOARD_WRITE_MAX_BYTES);
+    expect(validateClipboardWriteText(text)).toBe(text);
+  });
+
+  it("rejects empty, non-string and oversized payloads", () => {
+    expect(() => validateClipboardWriteText(" \n ")).toThrow(/leer/i);
+    expect(() => validateClipboardWriteText(4)).toThrow(/String/i);
+    expect(() => validateClipboardWriteText("x".repeat(CLIPBOARD_WRITE_MAX_BYTES + 1))).toThrow(/zu groß/i);
+  });
+});