feat: add combo skill system with 5 combos

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

combat/combo_test.go

@@ -0,0 +1,45 @@
+package combat
+
+import (
+	"testing"
+
+	"github.com/tolelom/catacombs/entity"
+)
+
+func TestDetectCombo_IceShatter(t *testing.T) {
+	actions := map[string]ComboAction{
+		"mage":    {Class: entity.ClassMage, ActionType: "skill"},
+		"warrior": {Class: entity.ClassWarrior, ActionType: "attack"},
+	}
+	combos := DetectCombos(actions)
+	if len(combos) == 0 {
+		t.Fatal("expected Ice Shatter combo")
+	}
+	if combos[0].Name != "Ice Shatter" {
+		t.Errorf("expected 'Ice Shatter', got %q", combos[0].Name)
+	}
+}
+
+func TestDetectCombo_NoMatch(t *testing.T) {
+	actions := map[string]ComboAction{
+		"w1": {Class: entity.ClassWarrior, ActionType: "attack"},
+		"w2": {Class: entity.ClassWarrior, ActionType: "attack"},
+	}
+	combos := DetectCombos(actions)
+	if len(combos) != 0 {
+		t.Errorf("expected no combos, got %d", len(combos))
+	}
+}
+
+func TestDetectCombo_Multiple(t *testing.T) {
+	// Healer skill + Warrior attack + Rogue item → Holy Assault + Restoration
+	actions := map[string]ComboAction{
+		"healer":  {Class: entity.ClassHealer, ActionType: "skill"},
+		"warrior": {Class: entity.ClassWarrior, ActionType: "attack"},
+		"rogue":   {Class: entity.ClassRogue, ActionType: "item"},
+	}
+	combos := DetectCombos(actions)
+	if len(combos) != 2 {
+		t.Errorf("expected 2 combos, got %d", len(combos))
+	}
+}