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/Customers.vue

@@ -0,0 +1,71 @@
+<template>
+  <h2>Customers</h2>
+
+  <div class="card">
+    <h3>Add customer</h3>
+    <div class="actions">
+      <input v-model="draft.name" placeholder="Name" />
+      <input v-model="draft.email" placeholder="Email" />
+      <button @click="add" :disabled="!draft.name || !draft.email">Add</button>
+    </div>
+  </div>
+
+  <table v-if="customers.length">
+    <thead>
+      <tr>
+        <th>ID</th>
+        <th>Name</th>
+        <th>Email</th>
+        <th></th>
+      </tr>
+    </thead>
+    <tbody>
+      <tr v-for="c in customers" :key="c.id">
+        <td>{{ c.id }}</td>
+        <td>{{ c.name }}</td>
+        <td>{{ c.email }}</td>
+        <td>
+          <button class="ghost" @click="remove(c.id)">Delete</button>
+        </td>
+      </tr>
+    </tbody>
+  </table>
+  <p v-else class="muted">No customers yet.</p>
+</template>
+
+<script setup>
+import { ref, onMounted, reactive } from "vue";
+import { api } from "../api.js";
+
+const customers = ref([]);
+const draft = reactive({ name: "", email: "" });
+
+async function load() {
+  customers.value = await api.listCustomers();
+}
+
+async function add() {
+  await api.createCustomer({ name: draft.name, email: draft.email });
+  draft.name = "";
+  draft.email = "";
+  await load();
+}
+
+async function remove(id) {
+  await api.deleteCustomer(id);
+  await load();
+}
+
+onMounted(load);
+</script>
+
+<style scoped>
+.actions input {
+  padding: 8px 10px;
+  border: 1px solid #334;
+  border-radius: 4px;
+  background: #0d1b2a;
+  color: var(--text);
+  min-width: 180px;
+}
+</style>