Add comprehensive existing file handling documentation to Create-Clip.md, Create-PillarBox.md, Create-Turnaround.md and Get-LastFrame.md explaining ffmpeg -y replacement behavior and WhatIf safety recommendations, expand SKILL.md prerequisites section to clarify Windows 11-only platform support with pwsh.exe requirement and reorganize core vs optional tools with task-specific check guidance, update conventions section to add Frames/Frame syntax tables and .skip marker behavior details, replace safety

skill/Get-LastFrame.md

@@ -104,6 +104,14 @@ Frame saved to: frame_0099.png
 # Creates: f_7.png
 ```
 
+## Existing Files
+
+An existing output PNG is **replaced** without a prompt. ffmpeg runs with `-y`.
+
+- When `-Image` contains a numbering token such as `%04d`, the file replaced is the **resolved** name, not the pattern. For example, `-Image f_%04d.png -Frame 3` writes and replaces `f_0003.png`.
+- If the output folder does not exist, it is created. With `-WhatIf` it is only reported.
+- Use `-WhatIf` first, or write to a new name.
+
 ## Safe Execution
 
 This script supports `-WhatIf` and `-Confirm` for safe execution: