Add Lichess loss analysis script

[metaember]

Summary

• Adds scripts/analyze_losses.py — downloads bot losses/draws from Lichess and categorizes errors
• For each bot move: runs custom engine, Stockfish at same depth, and Stockfish deep (ground truth)
• Classifies mistakes as depth issues (SF also misses at same depth) vs eval issues (SF finds it, engine doesn't)
• Verifies resignations were justified, flags draws where wins were missed

Usage

uv run --project scripts scripts/analyze_losses.py --since-hours 12 --verbose

Initial findings (12 games, last 12 hours)

• 82 mistakes, 16 blunders across 8 losses + 4 draws
• 59% eval issues vs 41% depth issues — evaluation function is the primary weakness
• 1 unjustified resignation (position was +274cp)
• 3 draws with missed wins (up to +504cp advantage squandered)

Test plan

• Ran on 1 game with --verbose to verify per-move output
• Ran on all 12 losses/draws from last 12 hours successfully
• JSON report output verified