bridge nel repo: sorgenti, unit systemd e istruzioni per i tester

- bridge/ con aira_bridge.py, setup_creds.py, aira_probe.py, test offline
- percorsi di configurazione via AIRA_CONFIG_DIR (default invariato)
- README del bridge in inglese: installazione, servizio, firewall, sicurezza
- README principale aggiornato (il bridge non è più 'fuori dal repo')

bridge/harbour-aira-bridge.service

@@ -0,0 +1,20 @@
+# Local HTTP bridge for the harbour-aira Sailfish app.
+# Install as a systemd *user* unit: see README.md in the same folder.
+[Unit]
+Description=Aira bridge for the harbour-aira app (local heat pump HTTP API)
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+# %h expands to the home of the user running the unit, so the file works as-is
+# for any user, provided the repo was cloned in ~/harbour-aira.
+WorkingDirectory=%h/harbour-aira/bridge
+# Must match the AIRA_CONFIG_DIR used when running setup_creds.py.
+Environment=AIRA_CONFIG_DIR=%h/.config/aira
+ExecStart=%h/harbour-aira/bridge/.venv/bin/python %h/harbour-aira/bridge/aira_bridge.py --host 0.0.0.0 --port 8790
+Restart=on-failure
+RestartSec=5
+
+[Install]
+WantedBy=default.target