feat(node): Add the --join flag to the run command to register and enroll in one step

[kaisoz]

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[gemini-code-assist]

Code Review

This pull request introduces a --join flag to the run command of sam-node, allowing users to enroll and start their node in a single step. It refactors the interactive login flow into a helper function, updates the quickstart documentation to highlight this new simplified flow, and promotes go-isatty to a direct dependency. Feedback on the changes points out that when --join is used in a non-interactive TTY environment, the hub address does not default to the community testnet as documented, and suggests updating the fallback logic to ensure consistency.

[gemini-code-assist]

When --join is set but there is no interactive TTY, the node starts an unauthenticated sidecar. However, if --hub is not explicitly changed, hubAddr remains set to the default production hub (node.DefaultHubURL), rather than defaulting to the community testnet (https://bananas.sam-mesh.dev) as documented. We should update hubAddr to the testnet URL in this non-interactive case to ensure consistency with the interactive flow.

					if !isatty.IsTerminal(os.Stdin.Fd()) {
						if !cmd.Flags().Changed("hub") {
							hubAddr = "https://bananas.sam-mesh.dev"
						}
						logger.Warn("--join set but no interactive TTY; starting unauthenticated sidecar for out-of-band enrollment")
					} else {