feat(perf): swap 4G->8G via second swapfile, applied live [#755]

Applied on my.knownelement.com 2026-09-03 (founder-approved):
/apps.swap2 4G, fstab-persisted, no restarts. Verification + closure
note: https://projects.knownelement.com/issues/755#note-13

README.md

@@ -45,3 +45,4 @@ SSH `root@my.knownelement.com` — routed through the KNEL/PFVCluster
 2026-09-02 (`~/.creds/cloudron.env`, refs only in this repo) — prefer the
 API over SSH for reads/limits; base image rebuilds (#710) still need SSH.
 - **Inotify headroom APPLIED 2026-09-03** (#755, founder-approved): `fs.inotify.max_user_instances` 128→1024 + `max_user_watches` →1048576 in the same sysctl file, after containerd/dockerd died of inotify exhaustion (full fleet resync 09:13–09:51). Runtime-applied, no daemon restarts; error stream dry from 10:08. OOM fail set complete: thefnf/grafana/projects bumped (1G/1G/1.5G), zero OOMs post-recovery.
+- **Swap 4G→8G APPLIED 2026-09-03** (#755, founder-approved): second swapfile `/apps.swap2` (4G, fstab-persisted, same-priority family) alongside the original `/apps.swap` — no swapoff, no restart, live `free -h` shows 8.0Gi. Idempotent applier: `perf/swap/grow-swap2.sh`. Headroom for the Monday app push.

perf/swap/grow-swap2.sh

@@ -0,0 +1,39 @@
+#!/bin/bash
+# grow-swap2.sh — add a second 4G swapfile on the Cloudron host [#755]
+# Founder-approved 2026-09-03. Second-file approach: no swapoff, no restart,
+# zero risk to the running fleet. Idempotent — safe to re-run.
+#
+# Applied live on my.knownelement.com 2026-09-03 (result: /apps.swap +
+# /apps.swap2 = 8G total, fstab persisted). Re-runnable on any host that
+# needs the same headroom; set NEW/SIZE_MB to taste.
+set -euo pipefail
+
+NEW=/apps.swap2
+SIZE_MB=4096
+
+if swapon --show=NAME --noheadings | grep -qx "$NEW"; then
+  echo "$NEW already active"
+else
+  if [ -e "$NEW" ]; then
+    echo "ERROR: $NEW exists but is not active — inspect manually" >&2
+    exit 1
+  fi
+  fallocate -l "${SIZE_MB}M" "$NEW" 2>/dev/null \
+    || dd if=/dev/zero of="$NEW" bs=1M count="$SIZE_MB" status=none
+  chmod 600 "$NEW"
+  mkswap "$NEW"
+  swapon "$NEW"
+  echo "activated $NEW"
+fi
+
+if grep -q "^$NEW " /etc/fstab; then
+  echo "fstab entry already present"
+else
+  printf '%s none swap sw 0 0\n' "$NEW" >> /etc/fstab
+  echo "fstab entry added"
+fi
+
+echo "--- swapon ---"
+swapon --show
+echo "--- free ---"
+free -h