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>

cfg/sample/ctrl/stop.sh

@@ -1,22 +1,15 @@
 #!/bin/bash
-# Stop all sample services
-# Usage: ./ctrl/stop.sh
+# Stop sample room
+
+set -e
 
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 ROOT_DIR="$(dirname "$SCRIPT_DIR")"
 
-echo "=== Stopping sample services ==="
+echo "=== Stopping sample ==="
 
-# Stop sample app
-if [[ -f "$ROOT_DIR/sample/docker-compose.yml" ]]; then
-    echo "Stopping sample app..."
-    cd "$ROOT_DIR/sample"
-    docker compose down
-fi
-
-# Stop soleprint
-echo "Stopping soleprint..."
-cd "$ROOT_DIR/soleprint"
-docker compose down
-
-echo "=== All services stopped ==="
+for d in "$ROOT_DIR/soleprint" "$ROOT_DIR/link" "$ROOT_DIR/sample"; do
+    if [[ -f "$d/docker-compose.yml" ]]; then
+        (cd "$d" && docker compose down)
+    fi
+done