[DEV-3526] Add automatic liquidity pipeline for ref payouts

[TaprootFreak]

Summary

• Automatically trigger LiquidityManagement pipeline when ref reward payouts lack sufficient liquidity
• Consistent with BuyCrypto implementation

Changes

• Add liquidityPipeline relation to RefReward entity
• Extend secureLiquidity() to check available liquidity before processing
• Start pipeline via liquidityService.buyLiquidity() when deficit detected
• Set status to PENDING_LIQUIDITY before pipeline attempt
• Process pending rewards when pipeline completes
• Reset to PREPARED on pipeline failure for automatic retry

Flow

PREPARED → [liquidity check] → PENDING_LIQUIDITY → [pipeline complete] → READY_FOR_PAYOUT
                                      ↓
                              [pipeline failed] → PREPARED (retry)

Test plan

• Test with sufficient liquidity → direct READY_FOR_PAYOUT
• Test with insufficient liquidity → pipeline started → PENDING_LIQUIDITY
• Test pipeline completion → READY_FOR_PAYOUT
• Test pipeline failure → reset to PREPARED