fix: melee attacks now apply enemy defenses (armor/barrier/dodge)

Bug: Melee sword attacks passed null as the enemy to applyEnemyDefenses,
causing all enemy defenses (armor, barrier, dodge) to be bypassed.
Spell damage and DoT effects correctly went through defenses.

Fix: In combat-actions.ts melee loop, get the current target enemy
from currentRoom.enemies (lowest HP, matching focus-fire targeting)
and pass it to applyEnemyDefenses instead of null.

Added 7 regression tests in melee-defense-bypass.test.ts to verify:
- Melee damage is reduced by armor
- Melee damage is reduced by barrier
- Unarmored enemies take more damage than armored ones
- Full damage dealt when no defenses
- Focus-fire targeting (lowest HP enemy)
- Graceful handling of empty enemy list
- Comparison proving defense application

All 948 tests pass (49 test files).

docs/circular-deps.txt

@@ -1,4 +1,4 @@
 # Circular Dependencies
-Generated: 2026-06-05T13:36:31.575Z
+Generated: 2026-06-06T14:50:40.350Z
 
 No circular dependencies found. ✅