feat: basic chord trainer

fix: don't add chords from backup if identical chords already exist, fixes #30

src/lib/backup/backup.ts

@@ -109,7 +109,11 @@ export function restoreFromFile(
 
 export function getChangesFromChordFile(file: CharaChordFile) {
   const changes: Change[] = []
+  const existingChords = new Set(get(chords).map(({phrase, actions}) => JSON.stringify({phrase, actions})))
   for (const [input, output] of file.chords) {
+    if (existingChords.has(JSON.stringify({actions: input, phrase: output}))) {
+      continue
+    }
     changes.push({
       type: ChangeType.Chord,
       actions: input,