The ChatGPT Codex models endpoint interprets `client_version` as a Codex
CLI compatibility version and filters models whose
`minimal_client_version` is newer. Zed was passing its unrelated
application version, so catalog contents depended accidentally on how
Zed's release number compared with Codex's version sequence.

A read-only sweep against the authenticated endpoint showed that
omitting the parameter returns HTTP 400, ordinary versions receive the
expected compatibility-filtered subsets, and `0.0.0` is a special
ungated sentinel. The `0.0.0` response had the same model set, ETag, and
canonical body hash as current and higher Codex versions, while `0.0.1`
returned no models.

This moves ownership of that behavior into `openai_subscribed::State`.
The normal constructor now always requests the ungated account catalog,
and the public constructor that accepted arbitrary host versions is
removed so applications cannot accidentally couple model visibility to
their own version scheme. The existing initial-load test pins the
resulting `client_version=0.0.0` request.

Testing performed:

- `cargo nextest run -p openai_subscribed`
- `cargo nextest run -p language_models openai_subscribed`
- `./script/clippy -p openai_subscribed -p language_models`
- `cargo fmt --all -- --check`
- `git diff --check`

Release Notes:

- Fixed ChatGPT subscription model discovery to avoid filtering models
by Zed's application version.