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

tools/setup-checks.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+# setup-checks.sh — deploy check scripts to /opt/oikos/checks on each host.
+# Auto-setup hook: tools/*.setup.sh runs after every git pull.
+set -euo pipefail
+
+CLONE_DIR="${HOMELAB_CONTEXT_DIR:-/opt/homelab}"
+CHECK_SETUP="$CLONE_DIR/checks/install.sh"
+
+if [ -f "$CHECK_SETUP" ]; then
+  bash "$CHECK_SETUP" || echo "[setup-checks] WARNING: install.sh exited with code $?"
+else
+  echo "[setup-checks] no checks/install.sh found, skipping"
+fi