feat: replace native confirm() with custom styled dialog

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

styles.css

@@ -408,6 +408,10 @@ nav{flex:1;overflow-y:auto;padding:4px 10px}
 .edit-pl-btn-cancel:hover{color:var(--text)}
 .edit-pl-btn-save{padding:10px 22px;border-radius:9px;border:none;background:var(--accent);color:#000;font-family:var(--font);font-size:14px;font-weight:700;cursor:pointer;transition:opacity .15s}
 .edit-pl-btn-save:hover{opacity:.85}
+.confirm-box{width:min(380px,calc(100vw - 24px));background:var(--surface);border:1px solid var(--border2);border-radius:18px;box-shadow:0 40px 80px rgba(0,0,0,.8);padding:28px 28px 20px}
+.confirm-title{font-size:17px;font-weight:700;margin-bottom:10px}
+.confirm-msg{font-size:14px;color:var(--text2);line-height:1.5;margin-bottom:24px}
+.confirm-footer{display:flex;justify-content:flex-end;gap:10px}
 @media(max-width:480px){.edit-pl-body{flex-direction:column;align-items:center}.edit-pl-cover-wrap{width:140px;height:140px}}
 
 /* ── SONG INFO MODAL ── */