Add Hunter's Edge

[radar]

Summary

• Implements Hunter's Edge (Core Set 2021): sorcery, {3}{G}, puts a +1/+1 counter on a creature you control, then that creature deals damage equal to its (post-counter) power to a creature you don't control.
• Two-target spell using the multi_target? / target_choices pattern (mirrors Primal Might), restricting target 1 to your creatures and target 2 to opponent's creatures.
• Counter is added and game.tick! runs before damage so power reflects the new counter; uses :deal_damage (one-way, not fight) so the targeted creature doesn't strike back.

Test plan

• bundle exec rspec spec/cards/hunters_edge_spec.rb (2 examples, 0 failures)
• bundle exec rspec full suite (617 examples, 0 failures)

Closes #199

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