Remove bbolt database dependency

Replaced bbolt-based database handling with Fyne built-in preferences for storing application settings. Deleted migration logic, database initialization, and error handling related to bbolt, simplifying the codebase and reducing external dependencies.

migration/migration.go

@@ -1,12 +0,0 @@
-package migration
-
-import (
-	"go.etcd.io/bbolt"
-)
-
-func Run(db *bbolt.DB) error {
-	return db.Update(func(tx *bbolt.Tx) error {
-		_, err := tx.CreateBucketIfNotExists([]byte("settings"))
-		return err
-	})
-}