fix: remove WIP folder contents from tracking and strengthen gitignore (#420)

The WIP/ directory was accidentally committed to main. Remove the
tracked file and update the gitignore entry from 'WIP' to 'WIP/' for
an explicit directory-only match, ensuring no WIP contents are ever
pushed regardless of filename.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: danielmeppiel

.gitignore

@@ -64,7 +64,7 @@ docs/wip/
 AGENTS.md
 PRD.md
 PRD*.md
-WIP
+WIP/
 # Internal planning documents
 skill-plan.md
 skill-strategy.md