Expose should not be playable when all enemies are both fortified and arcane immune

[eshaffer321]

Context

The fix for Expose being unplayable against fortified enemies (#833 or related) correctly makes Expose playable during the Ranged/Siege phase when enemies are fortified, since Expose's purpose is to remove fortification. However, there's an edge case with Arcane Immunity that should be handled.

Problem

When all enemies are both Fortified AND Arcane Immune, Expose (basic and powered) is truly useless:

• The fortification removal is blocked by Arcane Immunity
• The Ranged Attack can't hit because enemies are still fortified (fortification wasn't removed)

Currently, after the recent fix, Expose would still show as playable in this scenario.

Expected Behavior

Scenario	Playable?	Reason
All enemies fortified, at least one NOT arcane immune	Yes	Can remove fortification from non-immune enemy, ranged attack works on that target
All enemies fortified AND all arcane immune	No	Can't remove fortification (arcane immunity blocks it), can't ranged attack (still fortified)
At least one enemy NOT fortified (regardless of arcane immunity)	Yes	Ranged attack works on non-fortified enemy
All enemies arcane immune but at least one NOT fortified	Yes	Ranged attack works on the non-fortified enemy

Rules Reference

S1: Arcane Immunity — An enemy with Arcane Immunity does not lose its fortifications or its Resistances. The Ranged Attack, however, can be used normally against any enemy with Arcane Immunity.

The key insight: the Ranged Attack from Expose works fine against arcane immune enemies — the issue is only when those enemies are also fortified, since the fortification can't be removed.

Implementation Notes

This likely requires extending isRangedAttackUnusable() or effectIsRangedOnlyAttack() in core/src/engine/rules/effectDetection/combatEffects.ts to consider arcane immunity when evaluating whether enemy-targeting effects can actually bypass fortification. The check would need to verify that at least one fortified enemy is targetable (not arcane immune) before allowing the card.

Acceptance Criteria

• Expose (basic) is NOT playable when all enemies are fortified + arcane immune
• Expose (powered/Mass Expose) is NOT playable when all enemies are fortified + arcane immune
• Expose remains playable when at least one fortified enemy lacks arcane immunity
• Expose remains playable when at least one enemy is not fortified
• Tests cover all four scenarios in the table above