gitignore: exclude task management directory

This commit updates .gitignore to exclude the .tasks directory used for
local task tracking. This directory contains markdown files with task
metadata and is not intended to be committed to the repository.

Author: Roasbeef

.gitignore

@@ -58,3 +58,5 @@ btcutil/psbt/coverage.txt
 
 .DS_Store
 .aider*
+
+.tasks*