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>

config.example.toml

@@ -428,6 +428,18 @@ max_subagents = 10 # optional (1-20)
 # base_url = "https://api.together.xyz/v1"
 # model = "deepseek-ai/DeepSeek-V4-Pro"     # or deepseek-ai/DeepSeek-V4-Flash
 
+# ─────────────────────────────────────────────────────────────────────────────────
+# OpenAI Codex (ChatGPT) Provider — EXPERIMENTAL
+# Reuses your existing ChatGPT/Codex CLI OAuth login. Run `codex login` first;
+# CodeWhale reads and refreshes the access token from ~/.codex/auth.json. No API
+# key is stored here. Talks to the OpenAI Responses API at /codex/responses.
+# Env var aliases: OPENAI_CODEX_ACCESS_TOKEN / CODEX_ACCESS_TOKEN (token override),
+#   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
+[providers.openai_codex]
+# base_url = "https://chatgpt.com/backend-api"
+# model = "gpt-5.5"
+
 # ─────────────────────────────────────────────────────────────────────────────────
 # Web Search Provider
 # ─────────────────────────────────────────────────────────────────────────────────