Crea un nuevo push message para mostrar en el tray.

Body fields: message: str (required) — the message body min_version, max_version: str (optional) — semver bounds active: bool (default true) — if false, the row is created as a draft and NOT broadcast to live tunnels broadcast: bool (default true) — explicit override; set false to test message creation without pushing

Broadcast respects:

• active flag (no broadcast if active=false)
• broadcast flag (no broadcast if explicitly false)
• min_version / max_version bounds when applied to each tunnel's last_version (looked up from tunnel_tokens)

Caught in QA admin sweep 2026-04-10: previous version always broadcast immediately to ALL tunnels regardless of active or version filters, so an admin testing a draft message would push it to every live user.