core: implement yield snapshot background job

[EmeditWeb]

Problem

There is no yield snapshot background job. The product vision requires periodic yield/APY calculations, but no such job exists. The liquidity service computes APY as a weighted average from off-chain loan data rather than from actual contract yield.

User impact: The displayed APY is an estimate, not the actual yield earned by the pool. Sponsors may make decisions based on inaccurate yield data.

Before Starting

Read: context/architecture-context.md

Root Cause

The yield snapshot job was never implemented.

What To Build

1. Create src/jobs/yield-snapshot.processor.ts
2. Read pool share price from contract at regular intervals
3. Calculate APY from share price changes over time
4. Store yield snapshots in a yield_history table
5. Schedule: every 6 hours
6. Add GET /liquidity/yield-history endpoint to serve snapshots

Files To Touch

• src/jobs/yield-snapshot.processor.ts — new file
• src/jobs/jobs.module.ts — register processor
• src/modules/liquidity/liquidity.controller.ts — add yield-history endpoint

Acceptance Criteria

• Job runs every 6 hours
• Reads share price from contract
• Computes APY from share price change
• Stores in yield_history table
• GET /liquidity/yield-history returns snapshot data
• Build passes

Mandatory Checks

• context/ files read
• npm run build passes
• PR references this issue