Pure code movement. Every declaration of
internal/handlers/source_management.go moves unchanged into one of:
webhook_list.go, webhook_create.go, webhook_detail.go, webhook_edit.go
and webhook_delete.go for the webhook pages; event_log.go for the event
log; entrypoint.go for the entrypoint handlers; target_create.go and
target.go for the target handlers; and shared.go for the helpers
several of them use. Only each file's package line and imports are new.
Model: opus-5-5
