init: auto-reverse CLI with Python 3.14t, uv, and Nix flakes

Set up project scaffolding with free-threaded Python 3.14, uv for package
management, and Nix flakes for dev tooling (treefmt-nix with nixfmt/ruff,
pyright strict mode, direnv integration).

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

.gitignore

@@ -0,0 +1,16 @@
+# Python-generated files
+__pycache__/
+*.py[oc]
+build/
+dist/
+wheels/
+*.egg-info
+
+# Virtual environments
+.venv
+
+# Nix
+result
+
+# direnv
+.direnv