feat: add --dev flag to launch dev server after setup (v0.4.5)

[masonlet]

Summary

Adds a --dev/--no-dev flag that launches the project's dev server (npm run dev) in the foreground after setup completes.

Changes

• --dev / --no-dev flags with config-file support (dev/no_dev in ConfigEntry, resolved like other paired flags)
• watch/no_watch are now config-aware (previously CLI-only)
• New src/commands/dev.rs: dev-script detection + foreground dev server launch; dry-run assumes npm run dev
• Refactors:
  • read_package_json lifted out of mono/ into shared commands::npm (now takes a repo path directly)
  • Windows npm → cmd /c wrapping extracted into resolve_exe_args (shared by run_command)
• Windows dev server runs via PowerShell so Ctrl-C stops it cleanly (avoids cmd.exe's "Terminate batch job?" prompt)
• README: --dev docs, collapsible Installation/Workspace Structure sections, Config/Profile reorder