refactor(model): SpellBook을 SkillBook으로 리네이밍

- 게임 컨셉에 맞게 주문서 → 스킬북 용어 통일
- 관련 모든 참조 일괄 변경

lib/src/features/game/pages/skills_page.dart

@@ -10,15 +10,15 @@ import 'package:asciineverdie/src/features/game/widgets/active_buff_panel.dart';
 
 /// 스킬 페이지 (캐로셀)
 ///
-/// SpellBook 기반 스킬 목록과 활성 버프 표시.
+/// SkillBook 기반 스킬 목록과 활성 버프 표시.
 class SkillsPage extends StatelessWidget {
   const SkillsPage({
     super.key,
-    required this.spellBook,
+    required this.skillBook,
     required this.skillSystem,
   });
 
-  final SpellBook spellBook;
+  final SkillBook skillBook;
   final SkillSystemState skillSystem;
 
   @override
@@ -61,7 +61,7 @@ class SkillsPage extends StatelessWidget {
   }
 
   Widget _buildSkillsList(BuildContext context) {
-    if (spellBook.spells.isEmpty) {
+    if (skillBook.skills.isEmpty) {
       return Center(
         child: Text(
           L10n.of(context).noSpellsYet,
@@ -71,12 +71,12 @@ class SkillsPage extends StatelessWidget {
     }
 
     return ListView.builder(
-      itemCount: spellBook.spells.length,
+      itemCount: skillBook.skills.length,
       padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 4),
       itemBuilder: (context, index) {
-        final spell = spellBook.spells[index];
-        final skill = SkillData.getSkillBySpellName(spell.name);
-        final spellName = GameDataL10n.getSpellName(context, spell.name);
+        final skillEntry = skillBook.skills[index];
+        final skill = SkillData.getSkillBySpellName(skillEntry.name);
+        final skillName = GameDataL10n.getSpellName(context, skillEntry.name);
 
         // 쿨타임 상태 확인
         final skillState = skill != null
@@ -87,8 +87,8 @@ class SkillsPage extends StatelessWidget {
             !skillState.isReady(skillSystem.elapsedMs, skill!.cooldownMs);
 
         return _SkillRow(
-          spellName: spellName,
-          rank: spell.rank,
+          skillName: skillName,
+          rank: skillEntry.rank,
           skill: skill,
           isOnCooldown: isOnCooldown,
         );
@@ -100,13 +100,13 @@ class SkillsPage extends StatelessWidget {
 /// 스킬 행 위젯
 class _SkillRow extends StatelessWidget {
   const _SkillRow({
-    required this.spellName,
+    required this.skillName,
     required this.rank,
     required this.skill,
     required this.isOnCooldown,
   });
 
-  final String spellName;
+  final String skillName;
   final String rank;
   final Skill? skill;
   final bool isOnCooldown;
@@ -123,7 +123,7 @@ class _SkillRow extends StatelessWidget {
           // 스킬 이름
           Expanded(
             child: Text(
-              spellName,
+              skillName,
               style: TextStyle(
                 fontSize: 13,
                 color: isOnCooldown ? Colors.grey : null,