Replace the step list atomically

Sends the full ordered list of steps in one call — wipes the previous steps and reinserts. Steps are tiny; diffing is more trouble than it's worth.

Step kinds: • linkedin_connect — POST a connection request (with note) • linkedin_message — DM a 1st-degree connection • email — (v1.1) send via configured inbox • wait — no-op delay before the next step

Conditions (optional, NULL = always run): • after_accept — only run if the previous linkedin_connect step's invite has been accepted (signal.connection_accepted with outbound attribution) • no_reply_to_prev — only run if the lead hasn't replied since the previous step • never_replied — only run if the lead has never replied during this enrollment