refactor(qqbot): migrate qr onboard flow to sync + consolidate into onboard.py

- Replace async create_bind_task/poll_bind_result with synchronous
  httpx.Client equivalents, eliminating manual event loop management
- Move _render_qr and full qr_register() entry-point into onboard.py,
  mirroring the Feishu onboarding pattern
- Remove _qqbot_render_qr and _qqbot_qr_flow from gateway.py (~90 lines);
  call site becomes a single qr_register() import
- Fix potential segfault: previous code called loop.close() in the EXPIRED
  branch and again in the finally block (double-close crashed under uvloop)

gateway/platforms/qqbot/__init__.py

@@ -26,9 +26,8 @@ from .adapter import (  # noqa: F401
 # -- Onboard (QR-code scan-to-configure) -----------------------------------
 from .onboard import (  # noqa: F401
     BindStatus,
-    create_bind_task,
-    poll_bind_result,
     build_connect_url,
+    qr_register,
 )
 from .crypto import decrypt_secret, generate_bind_key  # noqa: F401
 
@@ -44,9 +43,8 @@ __all__ = [
     "_ssrf_redirect_guard",
     # onboard
     "BindStatus",
-    "create_bind_task",
-    "poll_bind_result",
     "build_connect_url",
+    "qr_register",
     # crypto
     "decrypt_secret",
     "generate_bind_key",