feat(cli): improve error messages for endpoint creation failures

[atihkin]

Summary

Improves CLI error messages when endpoint creation fails due to configuration issues. Addresses MLE-3108.

Changes

• Hardware error messages: Show specific reasons for failure (not compatible, unavailable, insufficient capacity, or config not supported with speculative decoding suggestion)
• Client-side validation: Validates min/max replicas, gpu-count, and availability-zone before API call
• Model errors: Better message when model not found or unavailable for dedicated endpoints
• Endpoint not found: Clear message with suggestion to list endpoints
• Permission errors: Clear access denied messages

Example Error Messages

Hardware unavailable:

Error: Cannot create endpoint with 8x H100 for model 'my-model'

The 8x H100 configuration is currently unavailable. This hardware type has no available capacity at this time.

Available hardware options for this model:
...

Hardware available but config fails:

Error: Cannot create endpoint with 8x H100 for model 'my-model'

Hardware is available but this configuration is not supported. Try adding --no-speculative-decoding.

Invalid replicas:

Error: --min-replicas (5) cannot be greater than --max-replicas (2)

Test plan

• Test with invalid hardware configuration
• Test with unavailable hardware
• Test with invalid min/max replicas
• Test with invalid gpu-count
• Test with invalid availability zone
• Test with non-existent model
• Test endpoint not found error

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