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/postrm

@@ -0,0 +1,41 @@
+#!/bin/bash
+set -e
+
+case "$1" in
+    remove)
+        # Service removed but config and user preserved
+        echo "Sensorpajen removed. Configuration preserved in /etc/sensorpajen/"
+        echo "To remove config: sudo rm -rf /etc/sensorpajen/"
+        
+        # Remove systemd service file
+        rm -f /etc/systemd/system/sensorpajen.service
+        systemctl daemon-reload || true
+        ;;
+
+    purge)
+        # Even on purge, we keep config by default (user can manually delete)
+        # This is safer as it prevents accidental data loss
+        echo "Configuration preserved in /etc/sensorpajen/"
+        echo "To remove config: sudo rm -rf /etc/sensorpajen/"
+        echo "To remove user: sudo userdel sensorpajen"
+        
+        # Remove systemd service file
+        rm -f /etc/systemd/system/sensorpajen.service
+        systemctl daemon-reload || true
+        
+        # Note: We intentionally do NOT remove:
+        # - /etc/sensorpajen (contains user data)
+        # - sensorpajen user (may own other files/processes)
+        # User must remove these manually if desired
+        ;;
+
+    upgrade|failed-upgrade|abort-install|abort-upgrade|disappear)
+        ;;
+
+    *)
+        echo "postrm called with unknown argument \`$1'" >&2
+        exit 1
+        ;;
+esac
+
+exit 0