chore: remove committed .superpowers agent artifacts, ignore local tooling dirs

Task briefs/reports and review diffs from the agent-driven snarkvm
migration (#44) are session workspace, not repo content. Ignore
.superpowers/, docs/superpowers/, and .worktrees/ so they cannot land
in a squash again.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: iamalwaysuncomfortable

.gitignore

@@ -9,3 +9,6 @@ tmp/
 *.pkl
 .idea/
 .claude/worktrees/
+.superpowers/
+docs/superpowers/
+.worktrees/