Add postgres backup script for alert-api DB

[MateoLostanlen]

Summary

Adds bin/backup_postgres.sh to dump the alert-api postgres DB to a local backups/ directory.

• Server IP resolved from Ansible inventory (no hardcoded IP)
• DB name and user read from the remote .env (no hardcoded creds)
• Falls back to pyro-ansible docker container if ansible-inventory isn't on PATH
• Writes to a temp file and only renames after pg_dump succeeds + size check passes
• backups/ is gitignored

Usage

make prepare
./bin/backup_postgres.sh