Initial project setup with Nix flake and gitignore

Nix devshell with gh, bubblewrap sandbox, and yolo mode.
Gitignore for .claude, .wave internals, secrets.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,11 @@
+.claude/*
+!.claude/commands/
+.archive/
+.idea/
+.wave/*
+!.wave/pipelines/
+!.wave/personas/
+!.wave/contracts/
+!.wave/prompts/
+wave.yaml
+.env