Add Link payment token vault commands

[rgarcia]

Summary

• add vaults payment-tokens create with browser/page checkout context and server-owned merchant binding
• remove mutable card updates and the explicit authorize invocation flow
• make items invoke ... fill accept guarded card bindings or selector-free payment-token fills
• surface connected-wallet descriptions and value-free fill instructions in human and safe JSON output
• expose card fallback only for the definitive lpt_not_supported response

Dependency

Depends on kernel/kernel#3950 being deployed. Raw request/response overrides keep this branch compatible with the currently released SDK while #3950's typed SDKs proceed through release.

Validation

• make test
• verified against kernel/kernel#3950's generated Go SDK preview

[kernel-internal]

🔧 CI Fix Available

I've pushed a fix for the CI failure on this PR.

What failed: make test never got past go vet — the replace directive pointing github.com/kernel/kernel-go-sdk at github.com/kernel/kernel-go-sdk-staging is unresolvable from CI, so every package importing the SDK failed to load.

The fix: drops the staging replace and builds against the released kernel-go-sdk v0.101.0, which is the switch the PR description already flags as required before merge. Three staging-only symbols were reworked using the raw-JSON techniques these files already rely on:

• kernel.FillVaultItemOperationRequestParam → param.Override[kernel.VaultItemPerformOperationParams] on the request body, mirroring how CreatePaymentToken builds its upsert params
• the fill result is read from result.RawJSON(), so printVaultOperationResult still sees the real response payload
• item.Description → a small vaultItemDescription helper reading description from the raw response, since the released SDK does not model that field

Behavior is unchanged: make test passes and all existing vault tests, including the fill request-payload and JSON output assertions, pass untouched.

👉 Click here to create a PR with the fix

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