Add FLE-style backtracking with AlphaEvolve integration

[bdougie]

Summary

• Adds BacktrackManager class that saves/restores game state via PyBoy save_state/load_state to escape stuck navigation (e.g. Route 1 y=28 blocker)
• Snapshots are taken on map changes and periodically; restores trigger when stuck_turns exceeds a configurable threshold
• Four new evolvable params (bt_max_snapshots, bt_restore_threshold, bt_max_attempts, bt_snapshot_interval) integrated into evolve.py scoring, perturbation, and mutation prompts
• Two new run_10_agents.py variants: aggressive_bt (low threshold, high retries) and no_bt (disabled baseline)

Test plan

• 415 tests pass (uv run pytest tests/)
• 100% coverage on all tracked modules
• uv run scripts/evolve.py <rom> --generations 3 --max-turns 2000 — verify backtracking params appear in genome
• uv run scripts/run_10_agents.py <rom> — compare backtrack-enabled vs disabled variants

Closes #5

[bdougie]

ROM Test Results

Ran the agent with backtracking enabled against the real ROM (--max-turns 500). Key findings:

Bug Found & Fixed: Backtrack guard was too narrow

The original guard (map_id == 40 AND party_count == 0) failed at the critical moment:

BT_DEBUG | in_lab=True map=40 party=0 stuck=20   # guard holds
BT_DEBUG | in_lab=False map=40 party=1 stuck=21   # party flips to 1 -> guard fails!
BACKTRACK | Restored to turn 50 map=0 (10,1)       # progress wiped

The agent picks up Charmander at ~turn 21 of being "stuck", but the backtrack guard immediately lets a restore through because party_count changed to 1. Fixed by guarding on map_id == 40 alone — the entire lab sequence (starter pickup + rival battle) is protected.

After fix: Full sequence works

MAP CHANGE | 0 -> 40 | Pos: (5, 3)          # Enter lab
LAB | phase 0→1 south at (5,4)               # Navigate to pokeball
LAB | phase 1→2 at pokeball column (7,4)
STUCK | ... Streak: 20                        # Pressing A at pokeball
OVERWORLD | Party: 1 | Stuck: 46             # Charmander acquired!
BATTLE | Player HP: 20/20 | Enemy HP: 20/20  # Rival battle starts
BATTLE | Player HP: 8/20 | Enemy HP: 0/20    # Rival defeated
MAP CHANGE | 40 -> 0 | Pos: (5, 11)          # Exit lab to Pallet Town

Also fixed: Oak trigger reverted to brute-force

The script-state-aware Oak trigger (reading 0xD5F1) was checking the lab script address while still on Pallet Town (map 0), where it's meaningless. Reverted to PR #10's proven approach: 4 rounds of mash_a(30) + wait(300).

Remaining: post-lab navigation

After exiting the lab, the agent gets stuck at (12,12) / (7,12) on Pallet Town instead of heading north to Route 1. This is a separate navigation issue, not related to backtracking.

Test suite

• 420 tests pass, 100% coverage