Add YouTube Music now-playing server, OBS overlay, and browser extension

Node.js server on port 9095 receives now-playing data via POST and broadcasts
to connected WebSocket clients. Includes a Firefox/Chrome extension that scrapes
YouTube Music's player bar every 3s, an OBS-ready transparent overlay with
animated equalizer bars, and an image proxy to bypass CDN restrictions in OBS.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

extension/popup.js

@@ -0,0 +1,50 @@
+// YTMusic Now Playing - Popup Script
+
+(function () {
+  "use strict";
+
+  const DEFAULT_SERVER_URL = "http://localhost:9095";
+  const serverUrlInput = document.getElementById("serverUrl");
+  const saveBtn = document.getElementById("save");
+  const statusEl = document.getElementById("status");
+
+  function setStatus(message, type) {
+    statusEl.textContent = message;
+    statusEl.className = `status-${type}`;
+  }
+
+  // Load saved URL on popup open
+  chrome.storage.sync.get({ serverUrl: DEFAULT_SERVER_URL }, (result) => {
+    serverUrlInput.value = result.serverUrl;
+    checkConnection(result.serverUrl);
+  });
+
+  // Save button handler
+  saveBtn.addEventListener("click", () => {
+    const url = serverUrlInput.value.trim().replace(/\/+$/, "");
+    if (!url) {
+      setStatus("Please enter a valid URL.", "err");
+      return;
+    }
+    chrome.storage.sync.set({ serverUrl: url }, () => {
+      setStatus("Saved!", "ok");
+      checkConnection(url);
+    });
+  });
+
+  // Check connection to the server
+  async function checkConnection(url) {
+    try {
+      const response = await fetch(`${url}/api/now-playing`, {
+        method: "GET",
+      });
+      if (response.ok) {
+        setStatus("Connected to server.", "ok");
+      } else {
+        setStatus(`Server returned ${response.status}.`, "err");
+      }
+    } catch (err) {
+      setStatus("Cannot reach server.", "err");
+    }
+  }
+})();