add fixture-invoicing example, sample-room wrap, kind cluster support

- examples/fixture-invoicing/: FastAPI + Vue + Postgres demo (4-entity invoice fixture)
- cfg/sample/: wraps the fixture (managed.repos points at examples/)
- ctrl/kind-{up,down,status}.sh + per-room k8s render in soleprint/ctrl/k8s/
- build.py: relative repo paths, resilient rmtree, optional k8s render hook
- cfg/.gitignore: stop ignoring sample/ and standalone/ template rooms

Manifests render cleanly but kind cluster has not been run end-to-end yet.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

examples/fixture-invoicing/frontend/src/api.js

@@ -0,0 +1,42 @@
+const apiBase = import.meta.env.VITE_API_URL || "";
+
+async function request(path, options = {}) {
+  const resp = await fetch(`${apiBase}${path}`, {
+    headers: { "Content-Type": "application/json" },
+    ...options,
+  });
+  if (!resp.ok) throw new Error(`${resp.status} ${resp.statusText}`);
+  if (resp.status === 204) return null;
+  return resp.json();
+}
+
+export const api = {
+  listCustomers: () => request("/api/customers"),
+  createCustomer: (data) =>
+    request("/api/customers", { method: "POST", body: JSON.stringify(data) }),
+  deleteCustomer: (id) => request(`/api/customers/${id}`, { method: "DELETE" }),
+
+  listInvoices: (params = {}) => {
+    const qs = new URLSearchParams(params).toString();
+    return request(`/api/invoices${qs ? "?" + qs : ""}`);
+  },
+  getInvoice: (id) => request(`/api/invoices/${id}`),
+  createInvoice: (data) =>
+    request("/api/invoices", { method: "POST", body: JSON.stringify(data) }),
+  deleteInvoice: (id) => request(`/api/invoices/${id}`, { method: "DELETE" }),
+
+  addLineItem: (invoiceId, data) =>
+    request(`/api/line-items/invoices/${invoiceId}`, {
+      method: "POST",
+      body: JSON.stringify(data),
+    }),
+  deleteLineItem: (id) =>
+    request(`/api/line-items/${id}`, { method: "DELETE" }),
+
+  recordPayment: (invoiceId, data) =>
+    request(`/api/payments/invoices/${invoiceId}`, {
+      method: "POST",
+      body: JSON.stringify(data),
+    }),
+  deletePayment: (id) => request(`/api/payments/${id}`, { method: "DELETE" }),
+};