Empty-leg Commons — cross-org marketplace

When you reposition an aircraft empty between two airports, you can publish that leg as a discounted charter on the Aviation Commons — a marketplace visible to every Turtini org running Aviation.

To list an empty leg:
1. Commons tab → "+ Publish empty leg"
2. Aircraft + departure/arrival airports + scheduled time
3. Asking price + minimum acceptable
4. Visibility — public (every Aviation org) or private (specific partner orgs you choose)
5. Save → live

Other operators see your listing in their Commons tab. They can request a quote (Wally: `aviation_quoteEmptyLeg`) or book directly. Booking sends the buying-org a confirmation and writes a charter booking on your side.

To shop the marketplace:
- Commons tab → browse by origin / destination / aircraft type / date.
- Wally: `aviation_listEmptyLegs` returns a quick list.

Platform fee on Commons transactions follows the standard rate (1–15%). The selling op gets the rest.