chore: add .git-blame-ignore-revs

Add the prettier reformat SHA so `git blame` skips the mechanical
whitespace-only change and points at the meaningful previous commit
instead. Contributors opt in locally with:

  git config blame.ignoreRevsFile .git-blame-ignore-revs

GitHub honours this file automatically in its blame UI.

Author: joshuaellis

.git-blame-ignore-revs

@@ -0,0 +1,6 @@
+# Bulk reformat commits — ignore in `git blame` to keep line history meaningful.
+# Configure once locally with:
+#   git config blame.ignoreRevsFile .git-blame-ignore-revs
+
+# chore(format): consolidate prettier configs — reformat sandboxes + __tests__ to root style
+397c97ec