test: the real-owner flag fails on any non-empty value other than 0; pin the lane's value; test the allowlist entry #816

Follow-ups from the reviews of #813 (the Docker lane fails when the real-owner case cannot run), non-blocking:

1. A mistyped flag must not skip silently. TPS_TEST_REQUIRE_REAL_OWNER is honoured only when it is exactly "1"; any other non-empty value takes the skip branch again. Treat any value other than unset, "" or "0" as required, or fail at module load on a value outside {0,1}, so a typo is red instead of green.
2. Pin the lane's value to the honoured value. Add an automated check (same pattern as real-flair-lane.test.ts's assertFlagReferences / assertRealFlairReport): the value docker-compose.yml sets is one the test honours, and the Docker lane's report has the real-owner case as passed, never skipped.
3. Test the allowlist entry. The scripts/test-home-guard.mjs entry that passes the flag to the test child has no test; add one.

Refs #801, #813.