fix: zenstack cli errors while using bun/bunx during docker build

[ErikMCM]

It's an obscure issue but it exists in my CI pipeline.

This PR attempts to fix the error that occurs when the following criteria are met:

1. Zenstack CLI commands are being ran on the Bun runtime
2. The terminal is non-TTY or not interactive (such as during docker build)
3. The REPL action is instantiated, requiring pretty-repl which subsequently requires repl which is not supported by the Bun runtime at this time

This PR fixes the error by:

1. Importing pretty-repl after checking if the runtime is bun and in a non-TTY terminal
2. Using bunx instead of npx within the zenstack generate command

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This PR could be reverted once Bun REPL support is fully implemented, allowing the zenstack repl command to be used in such a case. However, considering the current support for REPL on Bun is still experimental, it may be some time before it is resolved.

[ymc9]

Thank you for working on this @ErikMCM !