feat(channels): add QQ Official channel via Tencent Bot SDK

Implement QQ Official messaging channel using OAuth2 authentication
with Discord-like WebSocket gateway protocol for events.

- Add QQChannel with send/listen/health_check support
- Add QQConfig (app_id, app_secret, allowed_users)
- OAuth2 token refresh and WebSocket heartbeat management
- Message deduplication with capacity-based eviction
- Support both C2C (private) and group AT messages
- Integrate with onboard wizard, integrations registry, and channel
  list/doctor commands
- Include unit tests for user allowlist, deduplication, and config

src/integrations/registry.rs

@@ -143,6 +143,18 @@ pub fn all_integrations() -> Vec<IntegrationEntry> {
                 }
             },
         },
+        IntegrationEntry {
+            name: "QQ Official",
+            description: "Tencent QQ Bot SDK",
+            category: IntegrationCategory::Chat,
+            status_fn: |c| {
+                if c.channels_config.qq.is_some() {
+                    IntegrationStatus::Active
+                } else {
+                    IntegrationStatus::Available
+                }
+            },
+        },
         // ── AI Models ───────────────────────────────────────────
         IntegrationEntry {
             name: "OpenRouter",