v0.18.0:1 - scrub owner-specific hostnames, ips, usernames, names from tracked files

Replace real cluster IPs/hosts/usernames and example names with neutral
placeholders across docs, ops notes, package install text, and the offline
redaction test; delete the obsolete build-time starter prompt. Closes the
portability audit's single blocker. No runtime behavior change.

image/app/redaction/test_gateway.py

@@ -28,8 +28,8 @@ import scrub as R                       # noqa: E402  (vendored engine)
 import test_scrub_leak as REF           # noqa: E402  (reference fixtures)
 
 # Build the gateway app against a throwaway map store.
-os.environ.setdefault("SPARK1_HOST", "192.168.1.103")
-os.environ.setdefault("SPARK2_HOST", "192.168.1.87")
+os.environ.setdefault("SPARK1_HOST", "<spark-1-ip>")
+os.environ.setdefault("SPARK2_HOST", "<spark-2-ip>")
 from app.config import Settings                       # noqa: E402
 from app.redaction_gateway import build_router, MapStore  # noqa: E402