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/views/Invoices.vue

@@ -0,0 +1,93 @@
+<template>
+  <h2>Invoices</h2>
+
+  <div class="card">
+    <h3>Create invoice</h3>
+    <div class="actions">
+      <input v-model="draft.number" placeholder="Number (e.g. DEMO-2026-004)" />
+      <select v-model="draft.customer_id">
+        <option :value="null" disabled>Customer…</option>
+        <option v-for="c in customers" :key="c.id" :value="c.id">
+          {{ c.name }}
+        </option>
+      </select>
+      <button @click="add" :disabled="!draft.number || !draft.customer_id">
+        Create
+      </button>
+    </div>
+  </div>
+
+  <table v-if="invoices.length">
+    <thead>
+      <tr>
+        <th>#</th>
+        <th>Number</th>
+        <th>Customer</th>
+        <th>Issued</th>
+        <th>Status</th>
+      </tr>
+    </thead>
+    <tbody>
+      <tr v-for="inv in invoices" :key="inv.id">
+        <td>{{ inv.id }}</td>
+        <td>
+          <router-link :to="`/invoices/${inv.id}`" class="link">
+            {{ inv.number }}
+          </router-link>
+        </td>
+        <td>{{ customerName(inv.customer_id) }}</td>
+        <td>{{ inv.issued_at?.slice(0, 10) }}</td>
+        <td><span :class="['status', inv.status]">{{ inv.status }}</span></td>
+      </tr>
+    </tbody>
+  </table>
+  <p v-else class="muted">No invoices yet.</p>
+</template>
+
+<script setup>
+import { ref, onMounted, reactive, computed } from "vue";
+import { api } from "../api.js";
+
+const invoices = ref([]);
+const customers = ref([]);
+const draft = reactive({ number: "", customer_id: null });
+
+const customerById = computed(() =>
+  Object.fromEntries(customers.value.map((c) => [c.id, c]))
+);
+
+function customerName(id) {
+  return customerById.value[id]?.name || `#${id}`;
+}
+
+async function load() {
+  [invoices.value, customers.value] = await Promise.all([
+    api.listInvoices(),
+    api.listCustomers(),
+  ]);
+}
+
+async function add() {
+  await api.createInvoice({
+    number: draft.number,
+    customer_id: draft.customer_id,
+    status: "draft",
+  });
+  draft.number = "";
+  draft.customer_id = null;
+  await load();
+}
+
+onMounted(load);
+</script>
+
+<style scoped>
+.actions input, .actions select {
+  padding: 8px 10px;
+  border: 1px solid #334;
+  border-radius: 4px;
+  background: #0d1b2a;
+  color: var(--text);
+  min-width: 200px;
+}
+</style>