fix(proxy): retry silent bridge response.create upstreams

[Komzpa]

Summary

• retry an HTTP bridge request when the upstream Responses websocket accepts response.create but never emits response.created
• keep the existing fail-closed behavior when a request has already produced visible output or cannot be replayed safely
• add a regression test for the silent pre-created websocket case

Test plan

• uv run pytest tests/integration/test_http_responses_bridge.py -k 'missing_created_retry or precreated or response_create_gate or retired_gate'

[Komzpa]

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[Komzpa]

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[Komzpa]

Superseded: the core retry-before-claim idea landed via #1394 and #1563, and today's deployed #1625 covers the dead-owner recovery side. The remaining unique piece here (replaying client-owned anchors up to 20 times before response.created) is intentionally fenced off by the merged design, so closing this rather than rebasing it.