fix: perccli install — prefer apt, remove stale Dell download URL

The hardcoded dl.dell.com tarball URL is stale and returns a redirect.
Suggest 'apt install perccli' first (available in Proxmox repos), then
fall back to manual .deb download via dell.com/support with service tag.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/setup-guide.md

@@ -212,7 +212,15 @@ targets unconfigured physical disks.
 
 ### Install perccli
 
-Download from Dell support (search "PERCCLI") or copy the `.deb` to the host:
+Try apt first — it's in the Proxmox repos:
+
+```bash
+apt install -y perccli
+```
+
+If not found, download the `.deb` manually: go to `dell.com/support`, enter
+your service tag, then Drivers → Storage → search "PERCCLI", download the
+Linux package, copy it to the host, and install:
 
 ```bash
 dpkg -i perccli_*.deb

scripts/perc-nonraid.sh

@@ -10,9 +10,10 @@ set -euo pipefail
 
 PERCCLI=$(command -v perccli || command -v perccli64 || true)
 if [[ -z "$PERCCLI" ]]; then
-  echo "perccli not found. Install from:"
-  echo "  https://www.dell.com/support (search 'PERCCLI')"
-  echo "  or: dpkg -i perccli_*.deb"
+  echo "perccli not found. Install options:"
+  echo "  1. apt install -y perccli   (try this first — in Proxmox repos)"
+  echo "  2. Download from dell.com/support → enter service tag → Drivers → Storage"
+  echo "     Look for 'PERCCLI' and download the Linux .deb, then: dpkg -i perccli_*.deb"
   exit 1
 fi