Add .envrc to .gitignore

The .envrc file is auto-generated by Agent Mail and contains
machine-specific environment variables (workspace paths, agent names).
It should not be committed to the repository.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.gitignore

@@ -62,6 +62,9 @@ Thumbs.db
 # Ignore nix result
 result
 
+# direnv (machine-specific environment)
+.envrc
+
 # GoReleaser build artifacts
 dist/
 Formula/bd.rb