Secure giveaways

• /giveaway start with a prize, duration (like 30m, 6h, 3d), and winner count. It draws itself with cryptographic randomness when time is up.
• Entries are verified members only by default. Pro adds minimum account age and minimum trust score requirements.
• /giveaway end draws early; /giveaway reroll picks replacements, never repeating past winners.

Starting a giveaway is also on the dashboard, under Community, then Giveaways. Ending early and rerolling stay Discord-only for now: both need a live check against every entrant.