feat: localize all UI text to Korean

Translate all user-facing strings to Korean across 25 files:
- UI screens: title, nickname, lobby, class select, waiting, game,
  shop, result, help, leaderboard, achievements, codex, stats
- Game logic: combat logs, events, achievements, mutations, emotes,
  lobby errors, session messages
- Keep English for: class names, monster names, item names, relic names

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

entity/player_test.go

@@ -200,7 +200,7 @@ func TestBleedEffect(t *testing.T) {
 	p.AddEffect(ActiveEffect{Type: StatusBleed, Duration: 3, Value: 2})
 
 	msgs := p.TickEffects()
-	if len(msgs) == 0 || !strings.Contains(msgs[0], "bleed") {
+	if len(msgs) == 0 || !strings.Contains(msgs[0], "출혈") {
 		t.Error("expected bleed damage message")
 	}
 	if p.HP != startHP-2 {
@@ -231,7 +231,7 @@ func TestFreezeTickMessage(t *testing.T) {
 	p := NewPlayer("Test", ClassMage)
 	p.AddEffect(ActiveEffect{Type: StatusFreeze, Duration: 1, Value: 0})
 	msgs := p.TickEffects()
-	if len(msgs) == 0 || !strings.Contains(msgs[0], "frozen") {
+	if len(msgs) == 0 || !strings.Contains(msgs[0], "동결") {
 		t.Error("expected freeze message")
 	}
 	// Freeze duration 1 -> removed after tick