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>

bot/irc_client.py

@@ -18,16 +18,27 @@ from pathlib import Path
 
 from dotenv import load_dotenv
 
-load_dotenv()
+# ── Path resolution: deb install vs Docker/venv ────────────────────────────
+# If /etc/irc-bot exists we're running from a .deb package install.
+if os.path.isdir("/etc/irc-bot"):
+    _CONFIG_BASE = "/etc/irc-bot"
+    _DATA_BASE   = "/var/lib/irc-bot"
+    _LOG_BASE    = "/var/log/irc-bot"
+    load_dotenv("/etc/irc-bot/.env")
+else:
+    _CONFIG_BASE = "config"
+    _DATA_BASE   = "data"
+    _LOG_BASE    = "logs"
+    load_dotenv()
+
+os.makedirs(_LOG_BASE, exist_ok=True)
+os.makedirs(_DATA_BASE, exist_ok=True)
+os.makedirs(_CONFIG_BASE, exist_ok=True)
 
 # ── Logging ────────────────────────────────────────────────────────────────
 
-os.makedirs("logs", exist_ok=True)
-os.makedirs("data", exist_ok=True)
-os.makedirs("config", exist_ok=True)
-
 handler = logging.handlers.RotatingFileHandler(
-    "logs/bot.log", maxBytes=5 * 1024 * 1024, backupCount=3, encoding="utf-8"
+    os.path.join(_LOG_BASE, "bot.log"), maxBytes=5 * 1024 * 1024, backupCount=3, encoding="utf-8"
 )
 handler.setFormatter(
     logging.Formatter("%(asctime)s [%(levelname)s] %(message)s")
@@ -43,9 +54,9 @@ from bot.message_handler import handle_privmsg
 
 # ── Config ─────────────────────────────────────────────────────────────────
 
-CONFIG_PATH = "config/config.json"
-PID_PATH = "data/ircbot.pid"
-SOCK_PATH = "data/ircbot.sock"
+CONFIG_PATH = os.path.join(_CONFIG_BASE, "config.json")
+PID_PATH    = os.path.join(_DATA_BASE,   "ircbot.pid")
+SOCK_PATH   = os.path.join(_DATA_BASE,   "ircbot.sock")
 
 _config: dict = {}
 _config_lock = threading.Lock()

bot/memory.py

@@ -5,7 +5,11 @@ import re
 
 logger = logging.getLogger(__name__)
 
-HISTORY_DIR = "data/history"
+HISTORY_DIR = (
+    "/var/lib/irc-bot/history"
+    if os.path.isdir("/var/lib/irc-bot")
+    else "data/history"
+)
 
 
 def _sanitize_channel(channel: str) -> str: