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/link/main.py

@@ -0,0 +1,19 @@
+"""Link — DB bridge for the fixture invoicing app.
+
+Exposes a small HTTP API that wraps SQLAlchemy access to the fixture's
+postgres so soleprint tools can read/write without touching the app.
+"""
+
+from fastapi import FastAPI
+
+from adapters.sqlalchemy_bridge import router as db_router
+
+app = FastAPI(title="Link — Fixture Bridge")
+
+
+@app.get("/health")
+def health():
+    return {"status": "ok", "target": "fixture-invoicing"}
+
+
+app.include_router(db_router, prefix="/db")