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.

.env.example

@@ -13,6 +13,7 @@ WRENN_DIR=/var/lib/wrenn
 WRENN_HOST_INTERFACE=eth0
 WRENN_CP_URL=http://localhost:9725
 WRENN_DEFAULT_ROOTFS_SIZE=5Gi
+WRENN_FIRECRACKER_BIN=/usr/local/bin/firecracker
 
 # Auth
 JWT_SECRET=