Reduce verbosity of incus_bootstrap debug messages

## Description

The `incus_bootstrap` role has very detailed debug output messages (multi-paragraph troubleshooting guides embedded in `fail_msg` and `debug` blocks). While helpful for first-time users, this makes the role harder to maintain and the playbook output very noisy.

## Recommendation

- Move long troubleshooting text to a docs page or README
- Keep `fail_msg` concise (1-2 lines) with a link to the troubleshooting docs
- Use `verbosity` parameter on debug tasks so detailed output only shows with `-v`

## Priority

Low — cosmetic, doesn't affect functionality.