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/api/payments.py

@@ -0,0 +1,49 @@
+from fastapi import APIRouter, Depends, HTTPException
+from sqlalchemy.orm import Session
+
+from db import get_session
+from models import Invoice, Payment
+from schemas import PaymentIn, PaymentOut
+
+router = APIRouter()
+
+
+@router.get("", response_model=list[PaymentOut])
+def list_payments(
+    invoice_id: int | None = None, session: Session = Depends(get_session)
+):
+    query = session.query(Payment).order_by(Payment.paid_at.desc())
+    if invoice_id:
+        query = query.filter(Payment.invoice_id == invoice_id)
+    return query.all()
+
+
+@router.post("/invoices/{invoice_id}", response_model=PaymentOut, status_code=201)
+def record_payment(
+    invoice_id: int, payload: PaymentIn, session: Session = Depends(get_session)
+):
+    invoice = session.get(Invoice, invoice_id)
+    if not invoice:
+        raise HTTPException(404, "invoice not found")
+    payment = Payment(invoice_id=invoice_id, **payload.model_dump())
+    session.add(payment)
+
+    total_paid = sum(
+        (p.amount for p in invoice.payments), start=payment.amount
+    )
+    total_owed = sum((li.unit_price * li.quantity for li in invoice.line_items), start=0)
+    if total_owed > 0 and total_paid >= total_owed:
+        invoice.status = "paid"
+
+    session.commit()
+    session.refresh(payment)
+    return payment
+
+
+@router.delete("/{payment_id}", status_code=204)
+def delete_payment(payment_id: int, session: Session = Depends(get_session)):
+    payment = session.get(Payment, payment_id)
+    if not payment:
+        raise HTTPException(404, "payment not found")
+    session.delete(payment)
+    session.commit()