fix(scripts): reclaim space below 25 GiB instead of 20 GiB

Trigger the pre-zpool cache/kernel cleanup earlier (free < 25 GiB). On
small VPS hosts the kernel comes from the provider template and stale
kernel rollback is not a concern, so the extra headroom is worth it.

Co-authored-by: CommandCodeBot <noreply@commandcode.ai>

scripts/10-incus.sh

@@ -114,8 +114,8 @@ else
     # Without this, a host close to full would carve a pool that then starves
     # the root filesystem.
     FREE_KB=$(df -k --output=avail / | tail -1 | tr -d ' ')
-    if (( FREE_KB < 20 * 1024 * 1024 )); then
-      log "free space on / is $(( FREE_KB / 1024 / 1024 )) GiB (< 20 GiB) — reclaiming caches before sizing the pool..."
+    if (( FREE_KB < 25 * 1024 * 1024 )); then
+      log "free space on / is $(( FREE_KB / 1024 / 1024 )) GiB (< 25 GiB) — reclaiming caches before sizing the pool..."
       # Cleanest wins first; each is idempotent and never touches user data.
       DEBIAN_FRONTEND=noninteractive apt-get clean 2>/dev/null || true
       rm -rf /var/lib/apt/lists/* 2>/dev/null || true