Fix Bluetooth permission error with AmbientCapabilities and enhanced postinst

- Add AmbientCapabilities=CAP_NET_RAW CAP_NET_ADMIN to systemd service files
- Add sensorpajen user to bluetooth group in postinst
- Improve setcap error handling in postinst with clearer messaging
- Add comprehensive troubleshooting section for Bluetooth permission errors

This fixes the 'Operation not permitted' error when the service tries to
access Bluetooth hardware. The fix uses two layers of protection:
1. systemd AmbientCapabilities (modern, robust)
2. File capabilities via setcap (traditional, wider compatibility)

systemd/sensorpajen.service

@@ -12,21 +12,9 @@ ExecStart=%h/sensorpajen/.venv/bin/python -m sensorpajen.main
 Restart=always
 RestartSec=10
 
-# Bluetooth capabilities (alternative to setcap)
-# Note: This requires systemd to be run with proper permissions
-# If this doesn't work, use setcap on the Python binary instead
-#AmbientCapabilities=CAP_NET_RAW CAP_NET_ADMIN
-
-# Logging
-StandardOutput=journal
-StandardError=journal
-SyslogIdentifier=sensorpajen
-
-# Security
-# Note: NoNewPrivileges=true can prevent file capabilities from working
-# We need capabilities for Bluetooth access, so we can't use it
-#NoNewPrivileges=true
-PrivateTmp=true
+# Bluetooth capabilities
+AmbientCapabilities=CAP_NET_RAW CAP_NET_ADMIN
+NoNewPrivileges=false
 
 [Install]
 WantedBy=default.target