release: cli 0.6.26 + sandbox 0.2.39

[akirillo]

Summary

• release prime-sandboxes 0.2.39 with typed image listing from feat(sandboxes): add typed image listing #855 and the Connect RPC compatibility and sandbox-reachability fixes from fix(sandboxes): use compatible Connect RPC codec #854
• release Prime CLI 0.6.26 with prime images list backed by the typed sandbox SDK API
• publish the already-declared prime-sandboxes>=0.2.39 CLI dependency floor

This PR changes only the two package version strings. The main release risk comes from the sandbox SDK changes already reviewed in #854: VM command RPC encoding now uses the compatible Google protobuf codec, and creation waits surface local SDK failures instead of hiding them behind readiness timeouts. The image-listing path was validated against the live API for personal scope; the available key did not have permission to validate a successful platform-scope response.

Testing

• uv lock --check
• 87 focused SDK and CLI image-list tests
• 19 Connect RPC, command transport, and creation-reachability tests
• clean-wheel Connect RPC protobuf smoke test
• built prime==0.6.26 and prime-sandboxes==0.2.39 artifacts
• Ruff checks passed