build: gitignore docs/superpowers (local working notes)

Spec and implementation-plan files written by the brainstorming /
writing-plans skills are private working material. Keep them on
disk for ongoing reference but don't track them in git or push to
remotes.

Author: WZ

.gitignore

@@ -19,3 +19,6 @@ events.db-*
 *.jsonl
 *.jsonl.gz
 .env
+
+# Local working notes — design specs, implementation plans, etc.
+docs/superpowers/

README.md

@@ -82,7 +82,6 @@ internal/parser/     Anthropic Messages decoder + generic fallback
 internal/store/      JSONL + SQLite persistence
 internal/e2e/        End-to-end integration test
 testdata/flows/      Recorded flow fixtures
-docs/superpowers/    Spec + per-plan implementation plans
 ```
 
 ## Development