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>

soleprint/station/tools/graphgen/api.py

@@ -19,7 +19,10 @@ def _schema_paths() -> list[Path]:
     """Return ordered list of directories to search for schema."""
     paths = []
 
-    # cfg/<room>/station/tools/graphgen/   (room-specific, highest priority)
+    # station/tools/graphgen/   (room-merged schema.json lives here after build)
+    paths.append(SPR_ROOT / "station" / "tools" / "graphgen")
+
+    # cfg/<room>/station/tools/graphgen/   (source-tree room-specific, highest priority)
     cfg_dir = SPR_ROOT / "cfg"
     if cfg_dir.exists():
         for room in sorted(cfg_dir.iterdir()):