Add Ranger's Guile

[radar]

Summary

• Implements Ranger's Guile (Core Set 2021 reprint): instant, cost {G}, target creature you control gets +1/+1 and gains hexproof until end of turn.
• Uses the existing direct modifier pattern (Sure Strike / Heroic Intervention): target.modify_power(1), target.modify_toughness(1), target.grant_hexproof! — all default to until_eot: true.

Closes #209

Test plan

• bundle exec rspec spec/cards/rangers_guile_spec.rb — 2 examples, 0 failures
• bundle exec rspec — 617 examples, 0 failures

Tests cover:

• The +1/+1 buff and hexproof are applied to the targeted creature
• The keyword grant is marked until_eot?
• Both the P/T boost and hexproof wear off after end of turn

Co-Authored-By: Claude Opus 4.7 (1M context) noreply@anthropic.com