ax(mining): replace prose comments with usage examples in repository.go

Three comments violated AX Principle 2 (comments as usage examples):
- Repository interface comment described what it was rather than showing usage
- FileRepositoryOption comment said "configures a FileRepository" (restates the type)
- saveUnlocked comment described behaviour rather than showing the call pattern

Co-Authored-By: Charon <charon@lethean.io>

pkg/mining/repository.go

@@ -7,8 +7,8 @@ import (
 	"sync"
 )
 
-// Repository defines a generic interface for data persistence.
-// Implementations can store data in files, databases, etc.
+// var repo Repository[MinersConfig] = NewFileRepository[MinersConfig](path)
+// data, err := repo.Load()
 type Repository[T any] interface {
 	// data, err := repo.Load()
 	Load() (T, error)
@@ -28,7 +28,7 @@ type FileRepository[T any] struct {
 	defaults func() T
 }
 
-// FileRepositoryOption configures a FileRepository.
+// repo := NewFileRepository[MinersConfig](path, WithDefaults(defaultMinersConfig), myOption)
 type FileRepositoryOption[T any] func(*FileRepository[T])
 
 // repo := NewFileRepository[MinersConfig](path, WithDefaults(defaultMinersConfig))
@@ -83,7 +83,7 @@ func (r *FileRepository[T]) Save(data T) error {
 	return r.saveUnlocked(data)
 }
 
-// saveUnlocked saves data without acquiring the lock (caller must hold lock).
+// r.mutex.Lock(); defer r.mutex.Unlock(); return r.saveUnlocked(data)
 func (r *FileRepository[T]) saveUnlocked(data T) error {
 	dir := filepath.Dir(r.path)
 	if err := os.MkdirAll(dir, 0755); err != nil {