[Bug Bash] Check if typespec-autorest is installed when validating environment

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### Feedback

I was using the agent via agency. I had it validate my environment and it said everything was ok. But I hit a blocker later when I tried to generate an SDK locally (not in a pipeline) because @azure-tools/typespec-autorest was not installed.

The issue does not name a file or test. Start by locating the agency environment-validation entry point and the local SDK-generation dependency checks, then reproduce validation with typespec-autorest absent; done means validation reports the missing installation before generation is attempted.

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