refactor(qqbot): split qqbot.py into package & add QR scan-to-configure onboard flow

- Refactor gateway/platforms/qqbot.py into gateway/platforms/qqbot/ package:
  - adapter.py: core QQAdapter (unchanged logic, constants from shared module)
  - constants.py: shared constants (API URLs, timeouts, message types)
  - crypto.py: AES-256-GCM key generation and secret decryption
  - onboard.py: QR-code scan-to-configure API (create_bind_task, poll_bind_result)
  - utils.py: User-Agent builder, HTTP headers, config helpers
  - __init__.py: re-exports all public symbols for backward compatibility

- Add interactive QR-code setup flow in hermes_cli/gateway.py:
  - Terminal QR rendering via qrcode package (graceful fallback to URL)
  - Auto-refresh on QR expiry (up to 3 times)
  - AES-256-GCM encrypted credential exchange
  - DM security policy selection (pairing/allowlist/open)

- Update hermes_cli/setup.py to delegate to gateway's _setup_qqbot()
- Add qrcode>=7.4 dependency to pyproject.toml and requirements.txt

gateway/config.py

@@ -1229,12 +1229,12 @@ def _apply_env_overrides(config: GatewayConfig) -> None:
         qq_group_allowed = os.getenv("QQ_GROUP_ALLOWED_USERS", "").strip()
         if qq_group_allowed:
             extra["group_allow_from"] = qq_group_allowed
-        qq_home = os.getenv("QQ_HOME_CHANNEL", "").strip()
+        qq_home = os.getenv("QQBOT_HOME_CHANNEL", "").strip()
         if qq_home:
             config.platforms[Platform.QQBOT].home_channel = HomeChannel(
                 platform=Platform.QQBOT,
                 chat_id=qq_home,
-                name=os.getenv("QQ_HOME_CHANNEL_NAME", "Home"),
+                name=os.getenv("QQBOT_HOME_CHANNEL_NAME", "Home"),
             )
 
     # Session settings