Refactored to maintain a separate cloud version

Moves 12 packages from internal/ to pkg/ (config, id, validate, events, db,
auth, lifecycle, scheduler, channels, audit, service) so they can be imported
by the enterprise repo as a Go module dependency.

Introduces pkg/cpextension (shared Extension interface + ServerContext) and
pkg/cpserver (Run() entrypoint with functional options) so the enterprise
main.go can call cpserver.Run(cpserver.WithExtensions(...)) without duplicating
the 20-step server bootstrap. Adds db/migrations/embed.go for go:embed access
to OSS SQL migrations from the enterprise module.

cmd/control-plane/main.go is reduced to a 10-line wrapper around cpserver.Run.

pkg/events/event.go

@@ -0,0 +1,73 @@
+package events
+
+import (
+	"context"
+	"time"
+)
+
+// EventPublisher pushes events onto the notification stream.
+// Satisfied by *channels.Publisher.
+type EventPublisher interface {
+	Publish(ctx context.Context, e Event)
+}
+
+// ActorKind identifies what initiated an event.
+type ActorKind string
+
+const (
+	ActorUser   ActorKind = "user"
+	ActorAPIKey ActorKind = "api_key"
+	ActorSystem ActorKind = "system"
+)
+
+// Actor describes who triggered an event.
+type Actor struct {
+	Type ActorKind `json:"type"`
+	ID   string    `json:"id,omitempty"`
+	Name string    `json:"name,omitempty"`
+}
+
+// Resource identifies the object the event relates to.
+type Resource struct {
+	ID   string `json:"id"`
+	Type string `json:"type"`
+}
+
+// Event is the canonical notification payload published to the Redis stream
+// and delivered to channel subscribers.
+type Event struct {
+	Event     string   `json:"event"`
+	Timestamp string   `json:"timestamp"`
+	TeamID    string   `json:"team_id"`
+	Actor     Actor    `json:"actor"`
+	Resource  Resource `json:"resource"`
+}
+
+// Event type constants.
+const (
+	CapsuleCreated   = "capsule.created"
+	CapsuleRunning   = "capsule.running"
+	CapsulePaused    = "capsule.paused"
+	CapsuleDestroyed = "capsule.destroyed"
+	SnapshotCreated  = "template.snapshot.created"
+	SnapshotDeleted  = "template.snapshot.deleted"
+	HostUp           = "host.up"
+	HostDown         = "host.down"
+)
+
+// AllEventTypes is the complete set of valid event type strings.
+var AllEventTypes = []string{
+	CapsuleCreated,
+	CapsuleRunning,
+	CapsulePaused,
+	CapsuleDestroyed,
+	SnapshotCreated,
+	SnapshotDeleted,
+	HostUp,
+	HostDown,
+}
+
+// Now returns the current time formatted for event timestamps.
+func Now() string {
+	return time.Now().UTC().Format(time.RFC3339)
+}