feat: QR code scanning for gateway onboarding

iOS:
- QR scanner view using DataScannerViewController
- Photo library QR detection via CIDetector for saved QR images
- Deep link parser for openclaw://gateway URLs and base64url setup codes
- Onboarding wizard: full-screen welcome with "Scan QR Code" button,
  auto-connect on scan, back navigation, step indicators for manual flow

Backend:
- Add /pair qr action to device-pair extension for QR code generation
- TUI/WebUI differentiation: ASCII QR for TUI, markdown image for WebUI
- Telegram: send QR as media attachment via sendMessageTelegram
- Add data URI support to loadWebMedia for generic base64 media handling
- Export renderQrPngBase64 from plugin SDK for extension use

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/ios/Sources/Model/NodeAppModel.swift

@@ -457,6 +457,8 @@ final class NodeAppModel {
         switch route {
         case let .agent(link):
             await self.handleAgentDeepLink(link, originalURL: url)
+        case .gateway:
+            break
         }
     }