add ssh remove-key command

[vavo]

E-258: add ssh remove-key command

• resolves ssh: add remove-key command to manage SSH keys #258 by adding runpodctl ssh remove-key with --name and --fingerprint.
• maintains full legacy command compatibility (stderr warnings only, stdout unchanged).
• keeps runpodctl as the primary binary; drop-in upgrade for existing users.
• expands ssh key management coverage via the existing graphql updateUserSettings path, including ambiguity handling for duplicate key names.
• updates ssh command docs and adds unit coverage for command wiring and graphql removal behavior.
• tests: full unit suite passed locally; live e2e is still blocked in this workspace because no runpod api key is configured.

Test plan:

• go test ./...
• go test -tags e2e ./e2e

[promptless]

Promptless prepared a documentation update related to this change.

Triggered by runpod/runpodctl#264

Added documentation for the new runpodctl ssh remove-key command, including usage examples and flag descriptions for --name and --fingerprint.

Review at https://app.gopromptless.ai/suggestions/9e287ca0-cd90-4e51-b161-1981e00a0c48

[vavo]

live verification completed with a real Runpod API key.

verified flow:

• build runpodctl
• ssh add-key with disposable key A
• ssh add-key with disposable key B
• ssh list-keys to resolve key B fingerprint
• ssh remove-key --name for key A
• ssh remove-key --fingerprint for key B
• ssh list-keys to confirm both keys were removed

result: pass

cleanup was performed immediately after verification.