feat: support every song difficulty including Easy and Normal

src/routes/+page.svelte

@@ -33,7 +33,7 @@
       </a>
       <a class="feature-card" href="/rating">
         <span class="feature-number">03</span>
-        <div><h3>리더 레이팅</h3><p>입력한 편성으로 레이팅을 높이기 좋은 가창곡의 Hard·Expert를 최대 20개 추천하고, 5개씩 비교합니다.</p></div>
+        <div><h3>리더 레이팅</h3><p>입력한 편성으로 레이팅을 높이기 좋은 가창곡의 모든 난이도를 최대 20개 추천하고, 5개씩 비교합니다.</p></div>
         <span class="arrow" aria-hidden="true">→</span>
       </a>
       <a class="feature-card" href="/data/boards">

src/routes/analysis/+page.svelte

@@ -25,7 +25,7 @@
   export let mode: 'analysis' | 'rating' = 'analysis';
 
   type CardRow = (typeof cardSummary.cards)[number];
-  type DifficultyKey = 'hard' | 'expert';
+  import { difficulties, difficultyLabel, isDifficulty, type DifficultyKey } from '$lib/data/difficulty.ts';
   type CollectionState = Record<string, { owned?: boolean; awakening?: number }>;
   type MemberBoards = Record<string, string[]>;
   type BoardCards = Record<string, Record<string, string>>;
@@ -333,7 +333,7 @@
     const state = JSON.parse(stored) as Partial<SavedAnalysisState>;
     if (!legacy && state.schemaVersion !== 2) return;
     if (typeof state.songId === 'string' && songs.some((song) => song.id === state.songId)) selectedSongId = state.songId;
-    if (state.difficulty === 'hard' || state.difficulty === 'expert') difficulty = state.difficulty;
+    if (isDifficulty(state.difficulty)) difficulty = state.difficulty;
     songScoreBonusOverride = normalizeSongScoreBonusOverride(state.songScoreBonusOverride);
 
     if (Array.isArray(state.cardIds) && state.cardIds.length === 5) {
@@ -901,7 +901,7 @@
   <header class="page-header">
     <div>
       <h1>{mode === 'rating' ? '리더 레이팅' : '배치 분석'}</h1>
-      <p class="page-description">{mode === 'rating' ? '입력한 편성으로 리더 가창곡의 Hard·Expert를 예상 레이팅 순으로 최대 20개 추천합니다. 결과는 5개씩 확인할 수 있습니다.' : '특정 악곡과 카드 조합에서 최고 점수를 낼 수 있는 스페셜 발동 순서와 빈도 감소 조합을 찾습니다.'}</p>
+      <p class="page-description">{mode === 'rating' ? '입력한 편성으로 리더 가창곡의 모든 난이도를 예상 레이팅 순으로 최대 20개 추천합니다. 결과는 5개씩 확인할 수 있습니다.' : '특정 악곡과 카드 조합에서 최고 점수를 낼 수 있는 스페셜 발동 순서와 빈도 감소 조합을 찾습니다.'}</p>
       {#if mode === 'analysis' && selectedChart && selectedChart.scoreCalibrationSource !== 'measured' && selectedChart.scoreCalibrationSource !== 'formula-v1'}
         <p class="calibration-warning" role="status"><strong>추정 점수 안내</strong> 이 악곡의 점수 계수는 실측값이 아니므로 실제 점수와 오차가 크게 발생할 수 있습니다.</p>
       {/if}
@@ -919,8 +919,7 @@
       <div class="song-picker-field"><SongPicker {charts} {difficulty} bind:value={selectedSongId} on:change={() => result = null} /></div>
       <label>난이도
         <select bind:value={difficulty} on:change={() => result = null}>
-          <option value="expert">Expert</option>
-          <option value="hard">Hard</option>
+          {#each difficulties as value}<option {value}>{difficultyLabel(value)}</option>{/each}
         </select>
       </label>
       <label>가창 보너스 덮어쓰기 (0~10%)
@@ -1036,7 +1035,7 @@
   {#if mode === 'analysis' || result}
   <section class="panel result" aria-labelledby="result-title">
     <div class="section-title"><div><span>{mode === 'rating' ? '03' : '02'}</span><h2 id="result-title">분석 결과</h2></div></div>
-    {#if mode === 'rating' && result}<p class="board-guide"><strong>{selectedChart?.title} · {difficulty === 'expert' ? 'Expert' : 'Hard'}</strong> · 종합력 {overallPower.toLocaleString('ko-KR')} · 가창 보너스 10%</p>{/if}
+    {#if mode === 'rating' && result}<p class="board-guide"><strong>{selectedChart?.title} · {difficultyLabel(difficulty)}</strong> · 종합력 {overallPower.toLocaleString('ko-KR')} · 가창 보너스 10%</p>{/if}
     {#if result}
       <div class="order-sections">
         <section class="order-section">

src/routes/combination/+page.svelte

@@ -41,7 +41,7 @@
   export let eventMode = false;
 
   type CardRow = (typeof cardSummary.cards)[number];
-  type DifficultyKey = 'hard' | 'expert';
+  import { difficulties, difficultyLabel, isDifficulty, type DifficultyKey } from '$lib/data/difficulty.ts';
   type CollectionState = Record<string, { owned?: boolean; awakening?: number }>;
   type MemberBoards = Record<string, string[]>;
   type BoardCards = Record<string, Record<string, string>>;
@@ -370,7 +370,7 @@
   function applySavedState(state: Partial<SavedState>): void {
     if (state.schemaVersion !== 1) throw new Error('Unsupported preset');
     if (typeof state.songId === 'string' && songs.some((song) => song.id === state.songId)) selectedSongId = state.songId;
-    if (state.difficulty === 'hard' || state.difficulty === 'expert') difficulty = state.difficulty;
+    if (isDifficulty(state.difficulty)) difficulty = state.difficulty;
     fixedCardIds = Array.from({ length: 4 }, (_, index) => cardById.has(state.fixedCardIds?.[index] ?? '') ? state.fixedCardIds![index] : '');
     candidateAwakening = normalizeAwakening(state.awakening);
     candidateGenerationBonus = typeof state.candidateGenerationBonus === 'number' && Number.isFinite(state.candidateGenerationBonus)
@@ -422,7 +422,7 @@
     return {
       schemaVersion: 2,
       songId: typeof state.songId === 'string' ? state.songId : '',
-      difficulty: state.difficulty === 'hard' ? 'hard' : 'expert',
+      difficulty: isDifficulty(state.difficulty) ? state.difficulty : 'expert',
       cardIds: cards.map((card) => card.id),
       awakenings: cards.map((_, index) => Number.isFinite(state.awakenings?.[index]) ? normalizeAwakening(state.awakenings?.[index]) : 0),
       fixedCooldownReductions: cards.map((_, index) => normalizeFixedReduction(state.fixedCooldownReductions?.[index])),
@@ -1140,7 +1140,7 @@
         <div><span>00</span><h2 id="baseline-title">기준 조합</h2></div>
         <strong>배치 분석 저장값</strong>
       </div>
-      <p class="baseline-condition">{baselineChartMetadata?.title} · {baselineState.difficulty === 'expert' ? 'Expert' : 'Hard'}</p>
+      <p class="baseline-condition">{baselineChartMetadata?.title} · {difficultyLabel(baselineState.difficulty)}</p>
       <div class="baseline-members">
         {#each baselineResult?.formationOrder ?? baselineState.cardIds as cardId, slot}
           <div><span>{slot + 1}</span><strong>{baselineCardLabel(cardId)}</strong></div>
@@ -1164,7 +1164,7 @@
     <div class="section-title"><div><span>01</span><h2 id="conditions-title">탐색 조건</h2></div><strong>{ownedCardsOnly ? (eventMode ? '보유 이벤트 후보 대상' : '보유 5성 대상') : (eventMode ? '5성 + 대상 멤버 전 레어리티' : '5성 전체 대상')}</strong></div>
     <div class="song-fields">
       <div class="song-picker-field"><SongPicker {charts} {difficulty} bind:value={selectedSongId} on:change={() => result = null} /></div>
-      <label>난이도<select bind:value={difficulty} on:change={() => result = null}><option value="expert">Expert</option><option value="hard">Hard</option></select></label>
+      <label>난이도<select bind:value={difficulty} on:change={() => result = null}>{#each difficulties as value}<option {value}>{difficultyLabel(value)}</option>{/each}</select></label>
       <div class="chart-meta"><span>길이 {selectedChart?.durationSeconds ?? 0}초</span><span>노트 {selectedChart?.totalNotes?.toLocaleString('ko-KR') ?? 0}개</span><span>점수 계수 · {scoreCalibrationLabel}</span></div>
     </div>
     <div class="candidate-fields">