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/start.sh

@@ -1,28 +1,45 @@
 #!/bin/bash
-# Start all sample services
-# Usage: ./ctrl/start.sh [-d]
+# Start sample room (fixture invoicing + link + soleprint)
+#
+# Usage:
+#   ./start.sh              # Start all (foreground, with nginx)
+#   ./start.sh -d           # Start all (detached)
+#   ./start.sh --no-nginx   # Skip nginx reverse proxy
+#   ./start.sh --build      # Rebuild images
+
+set -e
 
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 ROOT_DIR="$(dirname "$SCRIPT_DIR")"
+APP_DIR="$ROOT_DIR/sample"
+LINK_DIR="$ROOT_DIR/link"
+SPR_DIR="$ROOT_DIR/soleprint"
 
+BUILD=""
 DETACH=""
-if [[ "$1" == "-d" ]]; then
-    DETACH="-d"
+NGINX_OVERRIDE="-f docker-compose.nginx.yml"
+
+for arg in "$@"; do
+    case $arg in
+        -d|--detached) DETACH="-d" ;;
+        --build) BUILD="--build" ;;
+        --no-nginx) NGINX_OVERRIDE="" ;;
+    esac
+done
+
+# Ensure shared docker network exists (soleprint + managed app share it)
+NETWORK="$(grep -m1 '^NETWORK_NAME=' "$APP_DIR/.env" | cut -d= -f2)"
+docker network inspect "$NETWORK" >/dev/null 2>&1 || docker network create "$NETWORK"
+
+echo "=== Starting sample ==="
+
+# 1) Managed app (db + backend + frontend)
+(cd "$APP_DIR" && docker compose up -d $BUILD)
+
+# 2) Link bridge
+if [[ -f "$LINK_DIR/docker-compose.yml" ]]; then
+    (cd "$LINK_DIR" && docker compose --env-file "$APP_DIR/.env" up -d $BUILD)
 fi
 
-echo "=== Starting sample services ==="
-
-# Start soleprint
-echo "Starting soleprint..."
-cd "$ROOT_DIR/soleprint"
-docker compose up $DETACH &
-
-# Start sample app
-if [[ -f "$ROOT_DIR/sample/docker-compose.yml" ]]; then
-    echo "Starting sample app..."
-    cd "$ROOT_DIR/sample"
-    docker compose up $DETACH &
-fi
-
-wait
-echo "=== All services started ==="
+# 3) Soleprint (+ nginx sidebar injection)
+(cd "$SPR_DIR" && docker compose -f docker-compose.yml $NGINX_OVERRIDE up $DETACH $BUILD)