P1 HTTP numbered proof: intent, attempt ceiling, overflow disposal and closed-circuit concurrency #250

Under teaql-conformance#216 and the approved HTTP-01/07/09/11 contracts, add direct runtime-owned native tests for null Context and blank intent before I/O, an always-failing endpoint at bounded attempt ceilings, peer-observed disposal of an incomplete oversized response, and concurrent calls after a successful half-open probe. Test-only feature candidate; no main merge, release, tag, deployment or Actions enablement. Existing retained native results are not rewritten.