gnd: Match graph-cli output format for init --from-example

Update the init --from-example command to match graph-cli behavior:

- Add prompts for subgraph slug and directory when not provided,
  with graph-cli style confirmation output (✔ Subgraph slug · value)
- Use spinners for all steps instead of showing raw npm/pnpm output
- Add "Initialize networks config" step that creates networks.json
- Add "Update subgraph name and commands in package.json" step
- Add "Initialize subgraph repository" step with initial commit
- Run codegen after dependency installation
- Update "Next steps" message to match graph-cli format

Author: lutter