Rename main.py to email_forwarder.py and fix systemd variable expansion

- Rename main.py to email_forwarder.py for better readability
- Update systemd service to use  in ExecStart and EnvironmentFile,
  remove WorkingDirectory to fix expansion issues
- Update install.sh and README references
- Drop-in sets PROJECT_DIR for runtime expansion

Changes:
- File rename: main.py -> email_forwarder.py
- Service: ExecStart and EnvironmentFile now use
- Docs: Updated to reflect new script name

README.md

@@ -38,5 +38,5 @@ This will set up the virtual environment, systemd services, and provide post-ins
 ## Troubleshooting
 
 - Logs: `journalctl --user -u email_forwarder.service`
-- Test: `source venv/bin/activate && python main.py`
+- Test: `source venv/bin/activate && python email_forwarder.py`
 - Timezone issues: Adjust UTC offset in script if needed.

email_forwarder.service

@@ -2,9 +2,7 @@
 Description=Email Forwarder
 
 [Service]
-Type=oneshot
+ExecStart=${PROJECT_DIR}/venv/bin/python ${PROJECT_DIR}/email_forwarder.py
-WorkingDirectory=${PROJECT_DIR}
-ExecStart=${PROJECT_DIR}/venv/bin/python main.py
 ExecStartPost=/usr/bin/curl -fsS --retry 3 ${UPTIME_SUCCESS_URL}
 OnFailure=email_forwarder-fail-notify.service