feat(dataflow): support embedded Desktop sessions

[mlhiter]

Summary

• Upgrade DataFlow to the namespaced Sealos Desktop SDK and use the SDK session contract.
• Allow configured exact HTTP(S) parent origins to embed DataFlow through NGINX and Higress Ingress policies.

Sequence Diagram

sequenceDiagram
    participant Desktop
    participant Ingress
    participant DataFlow
    participant SDK
    Desktop->>Ingress: Load DataFlow in an iframe
    Ingress-->>Desktop: Return CSP for configured parent origin
    Desktop->>DataFlow: Initialize embedded application
    DataFlow->>SDK: Request session and language
    SDK-->>DataFlow: Return user and kubeconfig

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Verification

• pnpm run test (28 files, 200 tests)
• pnpm run typecheck, pnpm run lint, and pnpm run build
• go build ./...
• Cluster 62 Helm revision 3, Ready Pod, public health check, and CSP header validation