hub v0.37.0: offsite provisioning SLICE 1 — Cloud-API client + provisioning core

Hetzner storage-box provisioning against api.hetzner.com/v1 (NOT .cloud).
internal/hetznerapi (typed client + CloudAPI interface + Fake + WaitAction);
internal/offsite (Provisioner.ProvisionOffsite — idempotent by label, shared
sub-account/dedicated box, transient password, non-secret Descriptor,
fail-closed); one_time_secrets store (single-use Save/Consume); POST
/offsite/consume-password/{id} (customer-key auth, once); config-form Offsite
section → applyOffsite (502+no-save on error) → descriptor in ConfigJSON →
version bump. Token/passwords never logged/committed/in ConfigJSON. Tested vs a
faked Cloud API + fail-closed red-proof. NOT yet live-provisioned (needs the
dedicated-project scoped token; current token can delete ep0).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PSK5g6qYLknKj8u3QAFEr6

hub/internal/api/handler.go

@@ -244,6 +244,9 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	case r.Method == http.MethodGet && strings.HasPrefix(path, "/config/"):
 		customerID := strings.TrimPrefix(path, "/config/")
 		h.handleConfigRetrieve(w, r, customerID)
+	case r.Method == http.MethodPost && strings.HasPrefix(path, "/offsite/consume-password/"):
+		customerID := strings.TrimPrefix(path, "/offsite/consume-password/")
+		h.handleOffsiteConsumePassword(w, r, customerID)
 	case r.Method == http.MethodGet && strings.HasPrefix(path, "/artifacts/"):
 		customerID := strings.TrimPrefix(path, "/artifacts/")
 		h.handleArtifactManifest(w, r, customerID)