feat(domain): record deployment events

[ctxswitch]

Parent

Related to #1

What to build

Add Deployment Event recording to the domain model so lifecycle changes can be reviewed later instead of relying only on current status.

Acceptance criteria

• A Deployment Event records actor, timestamp, previous status, new status, and optional note.
• Created Deployment Requests include an initial event.
• The domain model can append events for later lifecycle changes.
• Tests cover initial event creation and appending events.

Blocked by

• feat(domain): define deployment request model #2