Fix systemd service: Add Bluetooth permissions troubleshooting

The service needs setcap on the Python binary to access Bluetooth.
Added verification steps to troubleshooting section.

systemd/README.md

@@ -139,7 +139,26 @@ systemctl --user restart sensorpajen
 ```
 
 ### Troubleshooting
+### Permission Denied Errors
 
+If you see `PermissionError: [Errno 1] Operation not permitted` in the logs:
+
+```bash
+# Verify Bluetooth capabilities are set on Python binary
+getcap ~/.local/share/virtualenvs/*/bin/python3.*
+
+# If not set, apply capabilities (adjust path to your venv):
+sudo setcap 'cap_net_raw,cap_net_admin+eip' $(readlink -f ~/sensorpajen/.venv/bin/python3)
+
+# Verify it was set:
+getcap $(readlink -f ~/sensorpajen/.venv/bin/python3)
+# Should show: cap_net_admin,cap_net_raw+eip
+
+# Restart the service
+systemctl --user restart sensorpajen
+```
+
+**Important**: Capabilities must be set on the **actual Python binary**, not symlinks. Use `readlink -f` to resolve the real path.
 #### Service Won't Start
 
 ```bash