Add TS6 clientinit version middleware and fix playNext retry bug

clientinit compatibility:
- Analyzed @honeybbq/teamspeak-client's clientinit: it already sends a
  clean 14-field payload without problematic fields (no badges,
  integrations, security_hash, etc.)
- The key difference vs NeteaseTSBot is client_version: our library
  sends 3.5.3, NeteaseTSBot sends 3.6.2. TS6 servers may reject
  older versions.
- Add ts6-compat.ts with CommandMiddleware that patches clientinit
  to use version 3.6.2 + matching ECDSA signature when connecting
  to detected TS6 servers
- Middleware is automatically applied when detectedProtocol === "ts6"

Pre-existing bug fix:
- Fix playNext() in instance.ts where successful retry still fell
  through to player.stop(), killing the just-started playback

https://claude.ai/code/session_016WhH58avUD9xy2dgADJgTh

src/ts-protocol/ts6-compat.test.ts

@@ -0,0 +1,45 @@
+import { describe, it, expect } from "vitest";
+import { ts6VersionMiddleware } from "./ts6-compat.js";
+
+describe("ts6-compat", () => {
+  it("patches clientinit version to 3.6.2", async () => {
+    const middleware = ts6VersionMiddleware("3.6.2");
+    let captured = "";
+    const next = async (cmd: string) => {
+      captured = cmd;
+    };
+    const handler = middleware(next);
+
+    const original =
+      "clientinit client_nickname=Bot client_version=3.5.3\\s[Build:\\s1587971024] " +
+      "client_platform=Windows client_version_sign=Kvmj7qX6wJCPI5GVT71samfmhz/bvs7M+OTXWB/JWxdQbxDe17xda7dzUWLX7pjvdJTqZmbse1HBmTxThPKvAg== " +
+      "client_key_offset=42 hwid=abc123";
+
+    await handler(original);
+
+    expect(captured).toContain("client_version=3.6.2\\s[Build:\\s1695203293]");
+    expect(captured).toContain(
+      "client_version_sign=4OH3unxjGNBYS5EN4RFNrEo3UJz2Jn5KW1JqMDh3Yy93mSd0IwPm3FBrv8hCJgLuv99y6yBSN7pOmOpFjDaCw=="
+    );
+    // Other fields preserved
+    expect(captured).toContain("client_nickname=Bot");
+    expect(captured).toContain("client_key_offset=42");
+    expect(captured).toContain("hwid=abc123");
+  });
+
+  it("does not modify non-clientinit commands", async () => {
+    const middleware = ts6VersionMiddleware("3.6.2");
+    let captured = "";
+    const handler = middleware(async (cmd) => {
+      captured = cmd;
+    });
+
+    const original = "sendtextmessage targetmode=2 msg=hello";
+    await handler(original);
+    expect(captured).toBe(original);
+  });
+
+  it("throws for unknown target version", () => {
+    expect(() => ts6VersionMiddleware("9.9.9")).toThrow("Unknown version");
+  });
+});