fix: salvage follow-ups for Weixin adapter (#6747)

- Remove sys.path.insert hack (leftover from standalone dev)
- Add token lock (acquire_scoped_lock/release_scoped_lock) in
  connect()/disconnect() to prevent duplicate pollers across profiles
- Fix get_connected_platforms: WEIXIN check must precede generic
  token/api_key check (requires both token AND account_id)
- Add WEIXIN_HOME_CHANNEL_NAME to _EXTRA_ENV_KEYS
- Add gateway setup wizard with QR login flow
- Add platform status check for partially configured state
- Add weixin.md docs page with full adapter documentation
- Update environment-variables.md reference with all 11 env vars
- Update sidebars.ts to include weixin docs page
- Wire all gateway integration points onto current main

Salvaged from PR #6747 by Zihan Huang.

cron/scheduler.py

@@ -44,7 +44,7 @@ logger = logging.getLogger(__name__)
 _KNOWN_DELIVERY_PLATFORMS = frozenset({
     "telegram", "discord", "slack", "whatsapp", "signal",
     "matrix", "mattermost", "homeassistant", "dingtalk", "feishu",
-    "wecom", "sms", "email", "webhook", "bluebubbles",
+    "wecom", "weixin", "sms", "email", "webhook", "bluebubbles",
 })
 
 from cron.jobs import get_due_jobs, mark_job_run, save_job_output, advance_next_run
@@ -234,6 +234,7 @@ def _deliver_result(job: dict, content: str, adapters=None, loop=None) -> Option
         "dingtalk": Platform.DINGTALK,
         "feishu": Platform.FEISHU,
         "wecom": Platform.WECOM,
+        "weixin": Platform.WEIXIN,
         "email": Platform.EMAIL,
         "sms": Platform.SMS,
         "bluebubbles": Platform.BLUEBUBBLES,