feat(feishu): add scan-to-create onboarding for Feishu / Lark

Add a QR-based onboarding flow to `hermes gateway setup` for Feishu / Lark.
Users scan a QR code with their phone and the platform creates a fully
configured bot application automatically — matching the existing WeChat
QR login experience.

Setup flow:
- Choose between QR scan-to-create (new app) or manual credential input (existing app)
- Connection mode selection (WebSocket / Webhook)
- DM security policy (pairing / open / allowlist / disabled)
- Group chat policy (open with @mention / disabled)

Implementation:
- Onboard functions (init/begin/poll/QR/probe) in gateway/platforms/feishu.py
- _setup_feishu() in hermes_cli/gateway.py with manual fallback
- probe_bot uses lark_oapi SDK when available, raw HTTP fallback otherwise
- qr_register() catches expected errors (network/protocol), propagates bugs
- Poll handles HTTP 4xx JSON responses and feishu/lark domain auto-detection

Tests:
- 25 tests for onboard module (registration, QR, probe, contract, negative paths)
- 16 tests for setup flow (credentials, connection mode, DM policy, group policy,
  adapter integration verifying env vars produce valid FeishuAdapterSettings)

Change-Id: I720591ee84755f32dda95fbac4b26dc82cbcf823

website/docs/user-guide/messaging/feishu.md

@@ -31,12 +31,25 @@ Set it to `false` only if you explicitly want one shared conversation per chat.
 
 ## Step 1: Create a Feishu / Lark App
 
+### Recommended: Scan-to-Create (one command)
+
+```bash
+hermes gateway setup
+```
+
+Select **Feishu / Lark** and scan the QR code with your Feishu or Lark mobile app. Hermes will automatically create a bot application with the correct permissions and save the credentials.
+
+### Alternative: Manual Setup
+
+If scan-to-create is not available, the wizard falls back to manual input:
+
 1. Open the Feishu or Lark developer console:
    - Feishu: [https://open.feishu.cn/](https://open.feishu.cn/)
    - Lark: [https://open.larksuite.com/](https://open.larksuite.com/)
 2. Create a new app.
 3. In **Credentials & Basic Info**, copy the **App ID** and **App Secret**.
 4. Enable the **Bot** capability for the app.
+5. Run `hermes gateway setup`, select **Feishu / Lark**, and enter the credentials when prompted.
 
 :::warning
 Keep the App Secret private. Anyone with it can impersonate your app.