scheduler: add ping + ssh-script check kinds, metrics refactor, 17 host check scripts

- Refactor executeCheck to return checkResult struct with metrics map
- Add ping check kind (ICMP reachability via system ping, macOS+Linux)
- Add ssh-script check kind (remote host exec via SSH, allowlisted scripts)
- Add threshold evaluation (warn/crit per metric from check config JSONB)
- Add inode tracking to disk check
- All 4 existing checks now return structured metrics
- 17 check scripts: cpu, memory, load, swap, disk_usage, disk_smart,
  updates, zfs, process, uptime, oom, journal, time, fd, docker_health,
  caddy_error_rate, backup_freshness
- Auto-deploy via tools/setup-checks.sh -> checks/install.sh on git pull
- Add ping to OpenAPI CheckKind enum and generated Go types

checks/swap_check.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+# swap_check.sh — swap usage percentage.
+set -euo pipefail
+
+if [ -r /proc/meminfo ]; then
+  SWAP_TOTAL=$(awk '/^SwapTotal:/ {printf "%d", $2}' /proc/meminfo)
+  SWAP_FREE=$(awk '/^SwapFree:/ {printf "%d", $2}' /proc/meminfo)
+elif [ "$(uname)" = "Darwin" ]; then
+  SP=$(sysctl vm.swapusage 2>/dev/null | awk '{print $4, $9}' | tr -d 'M' || echo "0 0")
+  SWAP_TOTAL=$(echo "$SP" | awk '{printf "%.0f", $1*1024}')
+  SWAP_FREE=$(echo "$SP" | awk '{printf "%.0f", ($1-$2)*1024}')
+else
+  SWAP_TOTAL=0
+  SWAP_FREE=0
+fi
+
+if [ "$SWAP_TOTAL" -eq 0 ]; then
+  echo "{\"health\":\"healthy\",\"metrics\":{\"swap_pct\":0}}"
+else
+  USED_PCT=$(awk "BEGIN {printf \"%.1f\", (1 - $SWAP_FREE/$SWAP_TOTAL)*100}")
+  echo "{\"health\":\"healthy\",\"metrics\":{\"swap_pct\":$USED_PCT}}"
+fi