chore: enforce LF line endings via .gitattributes, ignore .idea and .superpowers

Shell scripts checked out with CRLF on Windows (core.autocrlf=true) broke
the Docker entrypoint at container start. Force LF for all text files at
the git layer, matching the existing .editorconfig and Prettier settings.

.gitattributes

@@ -0,0 +1 @@
+* text=auto eol=lf

.gitignore

@@ -12,6 +12,7 @@ config/server.yaml
 /package
 .env
 .vscode
+.idea
 .env.*
 !.env.example
 vite.config.js.timestamp-*
@@ -40,3 +41,4 @@ translation-report.json
 CONTEXT.md
 docs/adr/
 docs/superpowers/
+.superpowers/