Add homelab dashboards: system, LLM, and UPS on one domain

Three dashboards served by one FastAPI app with a SQLite history store
(raw / 1m / 1h) and hand-written SVG charts: no Prometheus, no Grafana,
no CDN, no build step. Nothing is fetched from the internet at runtime.

* system: a stdlib-only agent (agent/host_agent.py) reports /proc and
  /sys counters; the dashboard turns them into rates over a labelled
  window, so every number says how it was measured.
* llm: gufo/llama.cpp and vLLM /metrics are parsed by an in-house
  exposition parser. Measured delta/elapsed throughput beats a native
  per-request gauge, and each value carries its provenance.
* ups: a NUT wire-protocol client plus health checks that name what
  they looked at. Commands are gated by NUT_ALLOW_ACTIONS,
  DASH_READ_ONLY and a DANGER confirmation, re-checked server-side.

Missing values render as n/a rather than 0, and an unconfigured source
answers 404 {"configured": false} without dialling anything, so "not
deployed here" never looks like an outage.

253 tests at 94% coverage against captured real fixtures; ruff and
pyright clean.

LLM-Generated: true

scripts/dev-server.sh

@@ -0,0 +1,65 @@
+#!/usr/bin/env bash
+# Local development server: start|stop|status|restart|logs|tunnel-check
+#
+#   ./scripts/dev-server.sh restart     # reads .env.dev if present, runs on DASH_PORT
+#
+# The server keeps running after this shell exits (nohup + pidfile) so you can browse it
+# while an agent works. Logs: data/logs/dev.log
+set -uo pipefail
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+cd "$ROOT"
+PIDFILE="$ROOT/data/dev-server.pid"
+LOG="$ROOT/data/logs/dev.log"
+mkdir -p "$ROOT/data/logs"
+
+running() { [ -f "$PIDFILE" ] && kill -0 "$(cat "$PIDFILE")" 2>/dev/null; }
+
+start() {
+  if running; then
+    echo "already running (pid $(cat "$PIDFILE")) — http://127.0.0.1:${DASH_PORT:-8090}"
+    return 0
+  fi
+  if [ -f "$ROOT/.env.dev" ]; then
+    set -a; . "$ROOT/.env.dev"; set +a
+    echo "loaded .env.dev"
+  fi
+  PORT="${DASH_PORT:-8090}"
+  nohup .venv/bin/dashboards >"$LOG" 2>&1 &
+  echo $! >"$PIDFILE"
+  sleep 3
+  if running && curl -sf -o /dev/null "http://127.0.0.1:${PORT}/api/health"; then
+    echo "started pid $(cat "$PIDFILE") — http://127.0.0.1:${PORT}"
+  else
+    echo "FAILED to start; last lines of $LOG:"
+    tail -20 "$LOG"
+    return 1
+  fi
+}
+
+stop() {
+  if running; then
+    kill "$(cat "$PIDFILE")" 2>/dev/null
+    sleep 1
+    echo "stopped"
+  else
+    echo "not running"
+  fi
+  rm -f "$PIDFILE"
+}
+
+case "${1:-start}" in
+  start) start ;;
+  stop) stop ;;
+  restart) stop; start ;;
+  status)
+    if running; then
+      echo "running pid $(cat "$PIDFILE")"
+      curl -s "http://127.0.0.1:${DASH_PORT:-8090}/api/health" \
+        | .venv/bin/python -c "import json,sys; d=json.load(sys.stdin); print('status:', d['status']); [print(' ', s['key'], 'ok' if s['ok'] else 'DOWN', (s['error'] or '')[:90]) for s in d['sources']]"
+    else
+      echo "not running"
+    fi ;;
+  logs) tail -n 40 "$LOG" ;;
+  *) echo "usage: $0 start|stop|restart|status|logs"; exit 2 ;;
+esac