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>

portal/app.py

@@ -7,7 +7,12 @@ from dotenv import load_dotenv
 from flask import Flask, abort, jsonify, redirect, render_template, request, url_for, send_file
 import io
 
-load_dotenv()
+if os.path.isdir("/etc/irc-bot"):
+    load_dotenv("/etc/irc-bot/.env")
+    _LOG_PATH = "/var/log/irc-bot/bot.log"
+else:
+    load_dotenv()
+    _LOG_PATH = _LOG_PATH
 
 app = Flask(__name__, template_folder="templates", static_folder="static")
 app.secret_key = os.getenv("PORTAL_SECRET_KEY", "changeme")
@@ -66,7 +71,7 @@ def action_reconnect():
 @app.route("/action/clear_log", methods=["POST"])
 def action_clear_log():
     try:
-        open("logs/bot.log", "w").close()
+        open(_LOG_PATH, "w").close()
     except Exception:
         pass
     return redirect(url_for("logs"))
@@ -164,7 +169,7 @@ def bot():
 @app.route("/logs")
 def logs():
     lines = []
-    log_path = "logs/bot.log"
+    log_path = _LOG_PATH
     if os.path.exists(log_path):
         with open(log_path, "r", encoding="utf-8", errors="replace") as f:
             all_lines = f.readlines()
@@ -174,7 +179,7 @@ def logs():
 
 @app.route("/logs/download")
 def logs_download():
-    log_path = "logs/bot.log"
+    log_path = _LOG_PATH
     if not os.path.exists(log_path):
         abort(404)
     return send_file(log_path, as_attachment=True, download_name="bot.log")
@@ -183,7 +188,7 @@ def logs_download():
 @app.route("/api/logs")
 def api_logs():
     lines = []
-    log_path = "logs/bot.log"
+    log_path = _LOG_PATH
     if os.path.exists(log_path):
         with open(log_path, "r", encoding="utf-8", errors="replace") as f:
             lines = f.readlines()[-200:]

portal/config_manager.py

@@ -7,9 +7,14 @@ import sys
 
 logger = logging.getLogger(__name__)
 
-CONFIG_PATH = "config/config.json"
-PID_PATH = "data/ircbot.pid"
-SOCK_PATH = "data/ircbot.sock"
+if os.path.isdir("/etc/irc-bot"):
+    CONFIG_PATH = "/etc/irc-bot/config.json"
+    PID_PATH    = "/var/lib/irc-bot/ircbot.pid"
+    SOCK_PATH   = "/var/lib/irc-bot/ircbot.sock"
+else:
+    CONFIG_PATH = "config/config.json"
+    PID_PATH    = "data/ircbot.pid"
+    SOCK_PATH   = "data/ircbot.sock"
 
 
 def load_config() -> dict: