Rename grapho to pal, add onboard command, fix interactive input

- Rename grapho → pal across entire codebase (CLI, NixOS module,
  flake, docs, config paths)
- Add `pal onboard` interactive setup wizard with 4 steps:
  device, config repo, sync, backups
- Shows current setup summary when re-running onboard on an
  existing installation with warnings about what will change
- Fix askConfirm/askInput to read from /dev/tty so interactive
  prompts work correctly
- Remove || operator usage in askConfirm (not reliable in Lux)
- Add pal package to nix develop shell
- Document ~/.config/pal/ directory structure in README

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

.gitignore

@@ -4,7 +4,7 @@ result-*
 .direnv/
 
 # Compiled binaries
-grapho
+pal
 *_test
 
 # Secrets (NEVER commit unencrypted secrets)