docs: add provider hub and model provider pages

docs/providers/openai.md

@@ -0,0 +1,63 @@
+---
+summary: "Use OpenAI via API keys or Codex subscription in Clawdbot"
+read_when:
+  - You want to use OpenAI models in Clawdbot
+  - You want Codex subscription auth instead of API keys
+---
+# OpenAI
+
+OpenAI provides developer APIs for GPT models. Codex supports **ChatGPT sign-in** for subscription
+access or **API key** sign-in for usage-based access. The Codex CLI caches login details in
+`~/.codex/auth.json` (or your OS credential store), which Clawdbot can reuse.
+
+## Option A: OpenAI API key (OpenAI Platform)
+
+**Best for:** direct API access and usage-based billing.
+Get your API key from the OpenAI dashboard.
+
+### CLI setup
+
+```bash
+clawdbot onboard --auth-choice openai-api-key
+# or non-interactive
+clawdbot onboard --openai-api-key "$OPENAI_API_KEY"
+```
+
+### Config snippet
+
+```json5
+{
+  env: { OPENAI_API_KEY: "sk-..." },
+  agents: { defaults: { model: { primary: "openai/gpt-5.2" } } }
+}
+```
+
+## Option B: OpenAI Code (Codex) subscription
+
+**Best for:** using ChatGPT/Codex subscription access instead of an API key.
+Codex cloud requires ChatGPT sign-in, while the Codex CLI supports ChatGPT or API key sign-in.
+
+Clawdbot can reuse your **Codex CLI** login (`~/.codex/auth.json`) or run the OAuth flow.
+
+### CLI setup
+
+```bash
+# Reuse existing Codex CLI login
+clawdbot onboard --auth-choice codex-cli
+
+# Or run Codex OAuth in the wizard
+clawdbot onboard --auth-choice openai-codex
+```
+
+### Config snippet
+
+```json5
+{
+  agents: { defaults: { model: { primary: "openai-codex/gpt-5.2" } } }
+}
+```
+
+## Notes
+
+- Model refs always use `provider/model` (see [/concepts/models](/concepts/models)).
+- Auth details + reuse rules are in [/concepts/oauth](/concepts/oauth).