feat: add unlock system with 3 unlockable contents

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

store/unlocks.go

@@ -0,0 +1,47 @@
+package store
+
+import (
+	bolt "go.etcd.io/bbolt"
+)
+
+var bucketUnlocks = []byte("unlocks")
+
+type UnlockDef struct {
+	ID          string
+	Name        string
+	Description string
+	Condition   string
+}
+
+var UnlockDefs = []UnlockDef{
+	{ID: "fifth_class", Name: "Fifth Class", Description: "Reach floor 10 or higher", Condition: "floor 10+"},
+	{ID: "hard_mode", Name: "Hard Mode", Description: "Clear the game with 3+ players", Condition: "3+ player clear"},
+	{ID: "mutations", Name: "Mutations", Description: "Achieve victory on floor 20", Condition: "floor 20 victory"},
+}
+
+func (d *DB) UnlockContent(fingerprint, unlockID string) (bool, error) {
+	key := []byte(fingerprint + ":" + unlockID)
+	alreadyUnlocked := false
+	err := d.db.Update(func(tx *bolt.Tx) error {
+		b := tx.Bucket(bucketUnlocks)
+		if b.Get(key) != nil {
+			alreadyUnlocked = true
+			return nil
+		}
+		return b.Put(key, []byte("1"))
+	})
+	return !alreadyUnlocked, err
+}
+
+func (d *DB) IsUnlocked(fingerprint, unlockID string) bool {
+	key := []byte(fingerprint + ":" + unlockID)
+	unlocked := false
+	d.db.View(func(tx *bolt.Tx) error {
+		b := tx.Bucket(bucketUnlocks)
+		if b.Get(key) != nil {
+			unlocked = true
+		}
+		return nil
+	})
+	return unlocked
+}