Show extension checksums in CLI output

[IlyaasK]

Summary

• show extension checksums in human-readable list output
• show the full checksum after extension get and upload operations
• document checksum metadata in the CLI command reference

Why

Kernel now exposes the checksum of the exact uploaded extension archive. Showing it in the CLI lets operators identify and verify durable extension artifacts without dropping to a raw API request.

Implementation

List output adds a compact checksum column. Get and upload output print the checksum outside the width-bounded table so the complete digest remains available in normal terminal output. Legacy extensions without a checksum render -; JSON output remains the unmodified SDK response.

Verification

• go test -short -timeout=2m ./...
• go vet ./...
• gofmt -l cmd
• git diff --check
• targeted mutation checks for list, get, and upload checksum output: 3/3 killed
• crap4go: changed functions remain below the repository's existing CRAP hotspots

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Note

Low Risk
Display-only CLI and docs changes around extension metadata; no auth, persistence, or API behavior changes.

Overview
Surfaces Kernel’s extension archive checksum in human-readable CLI output so operators can verify artifacts without raw API calls.

extensions list adds a Checksum column (missing values show - via util.FirstOrDash). extensions get and extensions upload print the full digest on its own line after the property table so long hashes aren’t clipped. Name/checksum empty-state handling is centralized with util.FirstOrDash instead of ad hoc - logic. --output json is unchanged (SDK response, including checksum). README extension commands are updated to mention checksum metadata.

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