feat: print suggested next steps after mutating commands

[angeloashmore]

Description

After a mutating command completes, print a short hint about what to do next. This helps discoverability — users don't need to know the full command tree to find the next logical action.

Examples:

Command	Suggested next step
type create	prismic field add <type> --to-type <id> / prismic type view <id>
slice create	prismic field add <type> --to-slice <id> / prismic slice connect <id>
field add *	prismic type view <id> or prismic slice view <id>
repo create	prismic init --repo <domain>
init	prismic type create / prismic sync
webhook create	prismic webhook set-triggers
token create	Add to .env
preview add	prismic preview set-simulator

Only mutating commands (create/add) need this — list/view/remove don't.