Add per-device routing long-tail: hosts, providers, routes, routing_rules

Storage + CRUD (migration 0006, model, id-keyed store, REST handlers) plus
compiler rendering: each section is owned by a device and projected into that
device's rendered config (hosts/providers/routes/routing_rules).

internal/server/resources.go

@@ -61,6 +61,7 @@ func (s *Server) mountResources(r chi.Router) {
 	})
 	s.mountNAT(r)
 	s.mountLongtail(r)
+	s.mountPerDevice(r)
 }
 
 // respondOne writes a single resource, mapping ErrNotFound to 404.
@@ -76,6 +77,15 @@ func respondOne(w http.ResponseWriter, v any, err error) {
 	writeJSON(w, http.StatusOK, v)
 }
 
+// respondCreated writes a 201 with the created resource, or 500 on error.
+func respondCreated(w http.ResponseWriter, v any, err error) {
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, err.Error())
+		return
+	}
+	writeJSON(w, http.StatusCreated, v)
+}
+
 // respondDelete maps a delete result to 204/404/500.
 func respondDelete(w http.ResponseWriter, err error) {
 	if err != nil {