Fix finance log double-counting of exchange balances

[TaprootFreak]

Summary

• The finance log used Amount (total balance incl. locked funds) as the liquidity base and added pending exchange orders (exchangeOrder) on top
• For exchanges like Scrypt where Amount includes funds locked for pending withdrawals, this caused double-counting (~30k CHF overstatement, daily swings of up to 18x between min/max)
• Root cause: ExchangeAdapter.getForExchange() stored getTotalBalances() (which includes locked funds) in LiquidityBalance.amount, then log-job.service.ts added the same withdrawal amount again as pending exchangeOrder

Fix

• Add availableAmount field to LiquidityBalance entity (stores balance excluding locked funds)
• Add getAvailableBalances() to ScryptService (uses AvailableAmount) and ExchangeService (uses b.free)
• ExchangeAdapter now fetches and stores both amount (total) and availableAmount
• Finance log uses availableAmount as liquidity base — pending exchange orders then correctly compensate for the locked/in-transit portion
• Rule verification (rule.verify()) continues to use amount (total) — no behavioral change for deficit/redundancy detection

Trade-off

During active trading orders (buy/sell, typically <1 min), availableAmount is slightly lower since sell/buy aren't tracked in getPendingTx(). This is acceptable because trading orders fill in seconds, the valid flag threshold (5,000 CHF) catches brief outliers, and it self-corrects on the next cron run.

Test plan

• Build passes
• Lint passes
• Existing log-job.service.spec.ts tests pass (9/9)
• Verify on staging: finance log totalBalanceChf should stabilize (no more 3-18x daily swings)
• Verify rule verification still triggers correctly for actual deficits/redundancies

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