Shell hygiene: simpler reload, pyenv shim cleanup, ignore rules

- zshrc-dev: reload now execs a fresh zsh instead of re-sourcing
- zshenv: remove stale pyenv-rehash temp shim (>1min old) before init
- gitignore_global: ignore .claude/settings.local.json
- zshrc-natera: drop the git switch main->master wrapper

zshenv

@@ -21,5 +21,8 @@ fi
 if command -v pyenv 1>/dev/null 2>&1; then
   export PYENV_ROOT="$HOME/.pyenv"
   export PATH="$PYENV_ROOT/bin:$PATH"
+  # Clear a stale rehash temp file left behind by a killed pyenv-rehash.
+  # A real rehash completes in well under a second; anything older than a minute is stale.
+  find "$PYENV_ROOT/shims/.pyenv-shim" -mmin +1 -delete 2>/dev/null
   eval "$(pyenv init -)"
 fi