fix: support proxy authentication credentials in URL (closes #4)

Parse user:pass from proxy URLs into separate Playwright username/password
fields. Puppeteer wrapper strips credentials from --proxy-server and
auto-calls page.authenticate(). Bump Python 0.1.6, JS 0.1.3.

js/src/proxy.ts

@@ -0,0 +1,42 @@
+/**
+ * Shared proxy URL parsing for Playwright and Puppeteer wrappers.
+ */
+
+export interface ParsedProxy {
+  server: string;
+  username?: string;
+  password?: string;
+}
+
+/**
+ * Parse a proxy URL, extracting credentials into separate fields.
+ *
+ * Handles: "http://user:pass@host:port" -> { server: "http://host:port", username: "user", password: "pass" }
+ * Also handles: no credentials, URL-encoded special chars, socks5://, missing port.
+ */
+export function parseProxyUrl(proxy: string): ParsedProxy {
+  let url: URL;
+  try {
+    url = new URL(proxy);
+  } catch {
+    // Not a parseable URL (e.g. bare "host:port") — pass through as-is
+    return { server: proxy };
+  }
+
+  if (!url.username) {
+    return { server: proxy };
+  }
+
+  // Rebuild server URL without credentials
+  const server = `${url.protocol}//${url.hostname}${url.port ? `:${url.port}` : ""}`;
+
+  const result: ParsedProxy = {
+    server,
+    username: decodeURIComponent(url.username),
+  };
+  if (url.password) {
+    result.password = decodeURIComponent(url.password);
+  }
+
+  return result;
+}