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/backend/seed.py

@@ -0,0 +1,64 @@
+"""Seed obviously-fake demo data so the fixture is non-empty on first boot."""
+
+import logging
+from datetime import datetime, timedelta
+from decimal import Decimal
+
+from db import SessionLocal
+from models import Customer, Invoice, LineItem, Payment
+
+log = logging.getLogger(__name__)
+
+
+def seed_if_empty() -> None:
+    session = SessionLocal()
+    try:
+        if session.query(Customer).count() > 0:
+            return
+
+        log.info("Seeding fixture data…")
+        acme = Customer(name="Acme Widget Co.", email="billing@acme.example")
+        test = Customer(name="Test Customer 001", email="test@example.invalid")
+        session.add_all([acme, test])
+        session.flush()
+
+        inv1 = Invoice(
+            number="DEMO-2026-001",
+            customer_id=acme.id,
+            issued_at=datetime(2026, 1, 15),
+            due_at=datetime(2026, 2, 15),
+            status="sent",
+        )
+        inv2 = Invoice(
+            number="DEMO-2026-002",
+            customer_id=acme.id,
+            issued_at=datetime(2026, 2, 1),
+            due_at=datetime(2026, 3, 1),
+            status="paid",
+        )
+        inv3 = Invoice(
+            number="DEMO-2026-003",
+            customer_id=test.id,
+            issued_at=datetime(2026, 3, 10),
+            due_at=datetime(2026, 4, 10),
+            status="draft",
+        )
+        session.add_all([inv1, inv2, inv3])
+        session.flush()
+
+        session.add_all([
+            LineItem(invoice_id=inv1.id, description="Widget type A", quantity=10, unit_price=Decimal("19.99")),
+            LineItem(invoice_id=inv1.id, description="Widget type B", quantity=5, unit_price=Decimal("49.00")),
+            LineItem(invoice_id=inv2.id, description="Consulting (hours)", quantity=8, unit_price=Decimal("120.00")),
+            LineItem(invoice_id=inv3.id, description="Placeholder line item", quantity=1, unit_price=Decimal("0")),
+        ])
+
+        session.add_all([
+            Payment(invoice_id=inv2.id, amount=Decimal("960.00"), method="transfer", paid_at=datetime(2026, 2, 20)),
+            Payment(invoice_id=inv1.id, amount=Decimal("100.00"), method="card", paid_at=datetime(2026, 2, 1)),
+        ])
+
+        session.commit()
+        log.info("Seed complete.")
+    finally:
+        session.close()