Improve error messages for unsupported CPUs

## Goal
Better error messages when CPU is not fully supported.

## Current Behavior
Generic error messages that don't help users.

## Expected Behavior
- Clear message about which features are unsupported
- Suggest workarounds or alternatives
- Link to documentation

## Implementation
- Enhance cpu_diag.c output
- Add troubleshooting guide

## Use Case
Better user experience