test: add invalid-both-parts test for parseUntilSpec archive coverage

Add test for 'abc/def' input to parseUntilSpec — exercises the path at
lines 185-189 where both left AND right atoms of a slash-format are
unparseable (neither count nor duration), triggering ValidationError.

Author: BYK

test/commands/issue/archive.func.test.ts

@@ -201,6 +201,11 @@ describe("parseUntilSpec", () => {
   test("count/count → throws (right must be duration)", () => {
     expect(() => parseUntilSpec("10x/5x")).toThrow(ValidationError);
   });
+
+  test("invalid/invalid → throws when both parts are unparseable", () => {
+    // Both parts are unparseable atoms (not count, duration, or date)
+    expect(() => parseUntilSpec("abc/def")).toThrow(ValidationError);
+  });
 });
 
 // ── archiveCommand.func() integration tests ────────────────────────