Feature: Build liquidation auction system with Dutch auction mechanics

[devdianax]

Context

Liquidated collateral needs efficient price discovery. Current liquidation at fixed discount may not reflect market conditions.

Current Limitation/Problem

Liquidations execute at a fixed discount regardless of market depth or urgency, potentially leaving value on the table.

Expected Outcome

A Dutch auction liquidation system where collateral price starts at market value and decreases over time until a buyer steps in.

Acceptance Criteria

• Design Dutch auction: start price = oracle price, decrease linearly over auction duration
• Configurable auction parameters: duration, min price, discount floor
• Parallel auctions for concurrent liquidations
• Auction settlement: buyer repays debt + premium, receives collateral
• No-show auction: gradual discount increase until liquidator steps in
• Integration with liquidation bot for automated bidding
• Auction analytics: avg premium, time-to-fill, slippage distribution

Technical Scope

• contracts/lending-pool/src/liquidation/dutch_auction.rs - auction logic
• backend/src/bots/liquidator/auction-bidder.ts - automated bidder
• Prisma: AuctionEvent, AuctionSettlement models
• Edge cases: zero bids, oracle price change mid-auction, partial fills