Quickstart – Extension Normalization Command

Preview extension changes.
```
renamer extension .jpeg .JPG .jpg --dry-run
```
- Shows original → proposed paths.
- Highlights conflicts or “no change” rows for files already ending in .jpg.
Include nested directories or hidden assets when needed.
```
renamer extension .yaml .yml .yml --recursive --hidden --dry-run
```
- --recursive traverses subdirectories.
- --hidden opt-in keeps hidden files in scope.
Apply changes after confirming preview.
```
renamer extension .jpeg .JPG .jpg --yes
```
- --yes auto-confirms preview results.
- Command exits 0 even if no files matched (prints “no candidates found”).
Undo the most recent batch if needed.
```
renamer undo
```
- Restores original extensions using .renamer ledger entry.