fix: SSH docker host tunneling on Windows

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Summary

• Fix tunnel ssh docker host: create ssh tunnel tmp file: GetFileAttributesEx /tmp: The system cannot find the file specified. error when using docker context use with an SSH context on Windows
• On Windows, use TCP port forwarding (DOCKER_HOST=tcp://localhost:PORT) instead of Unix socket forwarding (DOCKER_HOST=unix://...), because Windows paths contain : which conflicts with SSH's -L local:remote delimiter
• On Linux/macOS, replace hardcoded /tmp with os.TempDir() (returns /tmp on these platforms, so no behavioral change)

Fixes #770

Related

• Docker context using SSH does not work #559 — SSH context not working (Linux/macOS, different root cause)
• Fix ssh context not working #577 — Open PR attempting to fix Docker context using SSH does not work #559 (does not address the Windows issue)
• feat: support ssh:// scheme for docker client host #268 — Original PR that introduced SSH support with hardcoded /tmp

What changed

pkg/commands/ssh/ssh.go

Two problems existed for Windows:

1. /tmp is hardcoded as the temp directory — does not exist on Windows
2. ssh -L <local_socket>:<remote_socket> uses : as delimiter — Windows paths like C:\Users\...\dockerhost.sock contain : which breaks the parsing

The fix introduces platform-aware tunneling by splitting createDockerHostTunnel into Unix and TCP variants:

• Windows (createDockerHostTunnelTCP): ssh -L localhost:<free_port>:/var/run/docker.sock with DOCKER_HOST=tcp://localhost:<port>
• Linux/macOS (createDockerHostTunnelUnix): ssh -L <tmpdir>/dockerhost.sock:/var/run/docker.sock with DOCKER_HOST=unix://<tmpdir>/dockerhost.sock (existing behavior, /tmp → os.TempDir())

Both variants share retrySocketDial/tryDial (added network parameter) and tunnelSSH (unchanged).

pkg/commands/ssh/ssh_test.go

• Updated existing test to be platform-aware (expects TCP on Windows, Unix socket on others)
• Added TestCreateDockerHostTunnelUnix — tests the Unix socket path directly
• Added TestCreateDockerHostTunnelTCP — tests the TCP port forwarding path directly
• Added error path tests for createDockerHostTunnelTCP (findFreePort failure, tunnelSSH failure)

Known limitations

• TCP tunnel on Windows binds to a localhost ephemeral port, which is accessible by any local process and has a small TOCTOU race window before ssh -L binds it.

Test plan

• go test ./pkg/commands/ssh/... passes on all platforms
• Windows + SSH docker context: lazydocker starts and connects successfully
• Linux/macOS + SSH docker context: no regression (behavior unchanged)
• Windows + local docker context: no impact (SSH tunnel code not triggered)