Initial commit: Sokoban 60-level game with A* solver

- sokoban.html: canvas game, entrance/exit door mechanic (level completes
  by walking to the exit after all boxes are placed, not an alert popup),
  solution search UI (modal with timer, cancel, "Решение найдено!" button)
- solver.js: A* with binary heap, true-distance heuristic, static
  deadlock cells, freeze-deadlock detection, tunnel macro-moves,
  chunked step() API for non-blocking search in the UI
- localStorage-backed solution leaderboard per level (fewest moves wins),
  fed by both solver finds and manual player completions; G replays the
  best recorded solution
- BACKLOG.md: known follow-ups (dead files, room/corral pruning, undo, etc.)

dynamic_prompt.txt

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