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

Three comments on Path, Exists, and Delete restated what the signatures
already convey. Replaced with concrete call examples per AX Principle 2.

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

pkg/mining/repository.go

@@ -133,12 +133,12 @@ func (r *FileRepository[T]) Update(fn func(*T) error) error {
 	return r.saveUnlocked(data)
 }
 
-// Path returns the file path of this repository.
+// path := repo.Path() // => "/home/user/.config/lethean-desktop/miners.json"
 func (r *FileRepository[T]) Path() string {
 	return r.path
 }
 
-// Exists returns true if the repository file exists.
+// if !repo.Exists() { return defaults, nil }
 func (r *FileRepository[T]) Exists() bool {
 	r.mu.RLock()
 	defer r.mu.RUnlock()
@@ -147,7 +147,7 @@ func (r *FileRepository[T]) Exists() bool {
 	return err == nil
 }
 
-// Delete removes the repository file.
+// if err := repo.Delete(); err != nil { return err }
 func (r *FileRepository[T]) Delete() error {
 	r.mu.Lock()
 	defer r.mu.Unlock()