Phase 8: Implement Debian package creation (2025-12-27)

- Create debian/ directory structure with all required files:
  - control: Package metadata and dependencies
  - compat: Debhelper compatibility level
  - changelog: Version history
  - rules: Build instructions
  - install: File installation mappings
  - postinst: Post-installation setup (user, venv, setcap)
  - prerm: Pre-removal script (stop service)
  - postrm: Post-removal script (cleanup, preserve config)
  - sensorpajen.service: System-wide systemd unit

- Update config.py to support dual-mode operation:
  - Auto-detects system installation (/opt/sensorpajen)
  - Uses /etc/sensorpajen for config in system mode
  - Falls back to PROJECT_ROOT/config for development

- Update scripts/approve-sensors.sh for system paths:
  - Detects system vs development installation
  - Uses correct venv and config paths

- Create scripts/verify-deb.sh: Automated build and verification

- Create debian/README.md: Comprehensive packaging documentation

Package features:
- System-wide installation to /opt/sensorpajen/
- Configuration in /etc/sensorpajen/ (preserved on upgrade/remove)
- Dedicated sensorpajen system user
- Automatic venv creation with dependencies
- Bluetooth capabilities set automatically
- Service auto-enabled but waits for config before starting
- Dual-mode code supports both system and development installations

debian/prerm

@@ -0,0 +1,27 @@
+#!/bin/bash
+set -e
+
+case "$1" in
+    remove|upgrade|deconfigure)
+        # Stop service before removal or upgrade
+        if systemctl is-active --quiet sensorpajen.service 2>/dev/null; then
+            echo "Stopping sensorpajen service..."
+            systemctl stop sensorpajen.service || true
+        fi
+
+        # Disable service on removal (not upgrade)
+        if [ "$1" = "remove" ]; then
+            systemctl disable sensorpajen.service || true
+        fi
+        ;;
+
+    failed-upgrade)
+        ;;
+
+    *)
+        echo "prerm called with unknown argument \`$1'" >&2
+        exit 1
+        ;;
+esac
+
+exit 0