Accept YouTube /live/ and /shorts/ URLs in extractVideoId

The video-id regex only matched /watch?v=, youtu.be, /embed/, and /v/
forms, so youtube.com/live/<id> and youtube.com/shorts/<id> links were
rejected with "Invalid YouTube URL". Add both forms to the server and
frontend extractors (kept in sync) and cover them with tests.

Ship as 0.2.159.

server/test/util.test.js

@@ -22,6 +22,17 @@ describe("extractVideoId", () => {
     assert.equal(extractVideoId("https://www.youtube.com/embed/dQw4w9WgXcQ"), "dQw4w9WgXcQ");
   });
 
+  test("extracts from /live/ URL (with ?si tracking param)", () => {
+    assert.equal(
+      extractVideoId("https://www.youtube.com/live/QEq1Fa-Br0U?si=CqlsUBpyTs_ksqi3"),
+      "QEq1Fa-Br0U"
+    );
+  });
+
+  test("extracts from /shorts/ URL", () => {
+    assert.equal(extractVideoId("https://www.youtube.com/shorts/dQw4w9WgXcQ"), "dQw4w9WgXcQ");
+  });
+
   test("accepts a bare 11-character id", () => {
     assert.equal(extractVideoId("dQw4w9WgXcQ"), "dQw4w9WgXcQ");
   });