feat(providers): finish OpenAI Codex (ChatGPT OAuth) provider and cut v0.8.55

Completes the in-progress OpenAI Codex provider and bumps the workspace to
0.8.55. Builds on the committed Together AI provider + model catalog work.

OpenAI Codex (ChatGPT) provider — experimental:
- Wire the previously-dead OAuth module into credential resolution. The TUI
  config now resolves the access token via the Codex CLI login in
  ~/.codex/auth.json (env overrides OPENAI_CODEX_ACCESS_TOKEN/CODEX_ACCESS_TOKEN),
  refreshing expired tokens synchronously via the OpenAI token endpoint —
  mirroring the existing Kimi OAuth flow rather than introducing a new pattern.
- Send the ChatGPT backend's required headers from the Responses client
  (chatgpt-account-id, OpenAI-Beta: responses=experimental, originator) and
  stop duplicating the Authorization header already installed on the client.
- Fix the cli crate's non-exhaustive ProviderKind matches (compile blocker).

Consistency / de-slop pass (so the provider fits the whole app, not one path):
- has_api_key_for / active_provider_has_config_api_key now detect the Codex
  OAuth login on disk, the same way they detect Kimi OAuth — a `codex login`
  user is no longer reported as unauthenticated.
- Replace the bogus OPENAI_CODEX_API_KEY hint (which exists nowhere else) with
  the real OPENAI_CODEX_ACCESS_TOKEN/CODEX_ACCESS_TOKEN in the auth-error and
  picker surfaces.
- Drop dead state in the Responses stream parser (unused ToolCallState fields /
  imports); tool-call data is streamed live.
- Update docs/PROVIDERS.md, config.example.toml, and the provider-metadata wire
  test for the Responses wire format.

Release:
- Bump workspace + crates + npm package to 0.8.55; update CHANGELOG.md and
  crates/tui/CHANGELOG.md.

Note: the live Responses round-trip has not been exercised against the
production ChatGPT backend in this environment; the provider ships as preview.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,29 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.8.55] - 2026-06-08
+
+### Added
+
+- **Together AI provider.** Added Together AI as a first-class provider
+  (`[providers.together]`, `TOGETHER_API_KEY`/`TOGETHER_BASE_URL`/`TOGETHER_MODEL`)
+  with default models `deepseek-ai/DeepSeek-V4-Pro` and
+  `deepseek-ai/DeepSeek-V4-Flash`, TUI provider-picker/auth/capability support,
+  and CLI `auth list`/`auth status` coverage.
+- **Model catalog updates.** Added Qwen 3.7 Max (`qwen/qwen3.7-max`), MiniMax 2.7
+  (`minimax/minimax-2.7`), and NVIDIA Nemotron 3 Ultra (`nvidia/nemotron-3-ultra`)
+  on OpenRouter.
+- **OpenAI Codex (ChatGPT) provider — experimental.** Added an `openai-codex`
+  provider that reuses an existing ChatGPT/Codex CLI OAuth login. The access
+  token is read and refreshed from `~/.codex/auth.json` (no API key is stored),
+  and requests use the OpenAI Responses API at `/codex/responses` with the
+  `chatgpt-account-id` header and `responses=experimental` beta opt-in. Env
+  overrides: `OPENAI_CODEX_ACCESS_TOKEN`/`CODEX_ACCESS_TOKEN`,
+  `OPENAI_CODEX_BASE_URL`/`CODEX_BASE_URL`, `OPENAI_CODEX_MODEL`/`CODEX_MODEL`,
+  `OPENAI_CODEX_ACCOUNT_ID`/`CODEX_ACCOUNT_ID`, `OPENAI_CODEX_AUTH_FILE`,
+  `CODEX_HOME`. Default model `gpt-5.5`. The live Responses round-trip has not
+  been exercised against the production backend in CI; treat as preview.
+
 ## [0.8.54] - 2026-06-08
 
 ### Added