Fix Arc Reactor restart: use bash for source, add systemd service, fix deploy

The admin panel restart command used shell_exec which runs /bin/sh (dash on
Ubuntu) — dash doesn't support 'source', so the venv never activated and the
reactor silently never started.

- admin/index.php: wrap restart in bash -c so 'source' works; try systemctl
  first then fall back to nohup
- deploy/jarvis-arc.service: add proper systemd unit so reactor auto-starts
  on boot and auto-restarts on crash
- deploy/jarvis-deploy.sh: install+enable service file when it changes; mkdir
  log dir before restart; fall back to nohup if systemctl not set up yet

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01X8tDRrQqgLjqXebMCBNcP3

deploy/jarvis-arc.service

@@ -0,0 +1,17 @@
+[Unit]
+Description=JARVIS Arc Reactor
+After=network-online.target mysql.service
+Wants=network-online.target
+
+[Service]
+Type=simple
+WorkingDirectory=/opt/jarvis-arc
+ExecStart=/opt/jarvis-arc/venv/bin/python3 /opt/jarvis-arc/reactor.py
+Restart=always
+RestartSec=10
+User=root
+StandardOutput=append:/home/jarvis.orbishosting.com/logs/arc_reactor.log
+StandardError=append:/home/jarvis.orbishosting.com/logs/arc_reactor.log
+
+[Install]
+WantedBy=multi-user.target