feat: implement fifty-move and seventy-five-move draw rules

[Mgrdich]

No description provided.

[Copilot]

Pull request overview

This pull request implements the fifty-move and seventy-five-move draw rules according to FIDE chess regulations. The fifty-move rule allows players to claim a draw after 100 half-moves (50 full moves) without a pawn move or capture, while the seventy-five-move rule automatically ends the game in a draw after 150 half-moves (75 full moves) under the same conditions.

Key changes:

• Added half-move clock management in applyMove() to reset on pawn moves or captures and increment otherwise
• Implemented draw detection logic in Status() with proper priority ordering (automatic draws before claimable draws)
• Added comprehensive test coverage for half-move clock behavior and both draw rules

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
internal/engine/board.go	Adds half-move clock increment/reset logic in the applyMove() method to track moves for the fifty-move and seventy-five-move rules
internal/engine/game_state.go	Updates Status() to detect both draw rules with correct thresholds (100 and 150 half-moves) and priority ordering; updates documentation to reflect completion of the feature
internal/engine/game_state_test.go	Adds comprehensive test coverage for half-move clock behavior (increment, reset on pawn moves, captures, en passant, and promotions) and both draw rule scenarios
context/spec/001-chess-engine-foundation/tasks.md	Marks Slice 12 tasks as completed

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