Add Debian .deb package support

- debian/control, changelog, conffiles — package metadata
- debian/postinst — creates irc-bot system user, installs Python venv,
  symlinks runtime dirs, enables systemd services
- debian/prerm/postrm — clean stop/uninstall with purge support
- debian/systemd/ — hardened systemd units for bot and portal
- build_deb.sh — assembles and builds the .deb via dpkg-deb
- Path resolver in irc_client.py, memory.py, config_manager.py, portal/app.py:
  uses /etc/irc-bot + /var/lib/irc-bot when installed as .deb, relative
  paths otherwise (Docker/venv unchanged)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

debian/systemd/irc-bot.service

@@ -0,0 +1,27 @@
+[Unit]
+Description=Active Blue IRC LLM Bot
+Documentation=http://192.168.1.64:3000/tocmo0nlord/irc-bot
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+User=irc-bot
+Group=irc-bot
+WorkingDirectory=/opt/irc-bot
+Environment="PYTHONPATH=/opt/irc-bot"
+EnvironmentFile=/etc/irc-bot/.env
+ExecStart=/opt/irc-bot/venv/bin/python -m bot.irc_client
+Restart=on-failure
+RestartSec=10
+StandardOutput=append:/var/log/irc-bot/bot.log
+StandardError=append:/var/log/irc-bot/bot.log
+
+# Hardening
+NoNewPrivileges=true
+PrivateTmp=true
+ProtectSystem=full
+ReadWritePaths=/etc/irc-bot /var/lib/irc-bot /var/log/irc-bot
+
+[Install]
+WantedBy=multi-user.target