Fix#605: Remove MATRIX_HOMESERVER, MATRIX_ACCESS_TOKEN, MATRIX_ROOM_ID from module-level globals.
Credentials are now read at call time in send_alert() via _read_env_value() to minimize
credential lifetime in process memory.
Fix#606: Update deploy.sh to use Infisical creds CLI instead of .secrets file.
Fetches NET_ALERTER_PASSWORD from matrix folder in Infisical vault, then generates
access token at deploy time.
All 16 net_alerter tests pass when run individually or in groups.
Cobra