tipjar/v1 package

Package tipjar is a public tip jar. Anyone can send real ugnot with an optional message via Tip; the realm keeps a running leaderboard of the most generous tippers and a feed of the most recent tips, both shown in Render. Only the deployer (captured as owner at init time) can Withdraw the accumulated balance. State-mutating functions are crossing functions (`cur realm`) per the gno 0.9 interrealm convention.