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/Create-Clip.md

@@ -151,6 +151,13 @@ This applies to every accepted container (`.mp4`, `.webm`, `.mkv`), matching is
 # Creates: P01-Clip.skip.mp4 scaled to 480p
 ```
 
+## Existing Files
+
+An existing derived clip is **replaced** without a prompt. The clip is created by [Clone-Video.ps1](Clone-Video.md), which runs ffmpeg with `-y` and overwrites its target.
+
+- The `.skip` marker stays last in the name that is replaced. For `P01.skip.mp4` the file replaced is `P01-Clip.skip.mp4`, or `P01-Clip<suffix>.skip.mp4` with `-Suffix`.
+- Use `-WhatIf` first, or use a different `-Suffix`.
+
 ## Safe Execution
 
 This script supports `-WhatIf` and `-Confirm` for safe execution (forwarded to `Clone-Video.ps1`):