Fix UnboundLocalError in _calculate_price_spreads (indentation bug, lines 760-775)

[OfficialGIGA]

Summary

Fixes a Python UnboundLocalError that fires continuously when running the arbitrage monitor with two or more exchange adapters.

Root cause

In core/services/arbitrage_monitor/implementations/arbitrage_monitor_impl.py around line 762, the spreads.append(...) call for the reverse-direction opportunity (buy exchange2 / sell exchange1) is indented outside its if book1["bid"] > book2["ask"]: guard.

When the condition is False, spread_abs and spread_pct are never assigned in that iteration, but the spreads.append(PriceSpread(... spread_abs=spread_abs ...)) call still executes and references them — raising UnboundLocalError.

This mirrors the structurally-correct block at lines 740-756 — the bug appears to be an accidental indentation slip.

Reproduction

1. Configure config/arbitrage/monitor.yaml with two exchanges (e.g. edgex, backpack)
2. Set monitor_only: true in config/arbitrage/arbitrage_segmented.yaml
3. Run python3 run_arbitrage_monitor.py in public-data mode
4. Within ~10 seconds, logs/arbitrage_monitor.log fills with error spam: ❌ 差价分析错误: cannot access local variable 'spread_abs' where it is not associated with a value — firing ~50 times per second on any pair where the bid/ask cross briefly.

Fix

Indent the spreads.append(...) block (and its timestamp=datetime.now() line) inside the if statement to match the mirror block at lines 740-756. Whitespace-only change — no logic modified.

Verification

After applying the patch:

• Zero spread_abs errors over 5+ minutes of live monitoring
• 27 overlapping pairs on edgex + backpack, ~20 opportunities/second detected cleanly
• Tested on Python 3.12.10, ccxt 4.5.58, websockets 15.0.1, macOS

Notes

• Comments in the modified block remain in Chinese (consistent with the rest of the file)
• No tests included as the project doesn't have a test harness for this module — happy to add one if there's a preferred pattern