Compute node hostname missing cluster prefix (install.py skips prefix for execute mode)

## Description

CCWS compute (execute) nodes get hostname `gpu-test-1` but the Slurm autoscaler generates `ccw-gpu-test-1` (with cluster prefix) in `azure.conf`. `slurmd` crash-loops because the names don't match. Login nodes are not affected.

## Root cause

In `/opt/cycle/jetpack/system/bootstrap/azure-slurm-install/install.py`, line ~1028:

```python
def set_hostname(s: InstallSettings) -> None:
new_hostname = s.node_name.lower()
if s.mode != "execute" and not new_hostname.startswith(s.node_name_prefix):
new_hostname = f"{s.node_name_prefix}{new_hostname}"
```

Execute nodes skip the prefix prepend (`if s.mode != "execute"`). But the autoscaler always generates names WITH the prefix (`ccw-gpu-test-1`).

Similarly, CCWS `01-rename_host.sh` only prepends the cluster prefix for login nodes (`if is_login`), not compute nodes.

The result: login → `ccw-login-1` (correct), compute → `gpu-test-1` (wrong).

## Steps to reproduce

1. Deploy CCWS with `NodeNameIsHostname=true` and `NodeNamePrefix="Cluster Prefix"`
2. Add a compute node via the autoscaler (submit a job)
3. Check hostname on the compute node: `hostname` → `gpu-test-1`
4. Check Slurm expects: `grep gpu /etc/slurm/azure.conf` → `ccw-gpu-test-1`
5. `slurmd` crash-loops with "lookup failure for node"

## Environment

- CycleCloud 8.8.3-3667
- Slurm 23.11.7
- Ubuntu 22.04

## Workaround

Cluster-init script that extends the `01-rename_host.sh` pattern to compute nodes: checks if `cyclecloud.node.name` already has the prefix (autoscaler-provisioned) and prepends if not (manually added).

## Related

- #323 (Port ccw set hostname logic)