docs: add provider hub and model provider pages

docs/providers/index.md

@@ -0,0 +1,40 @@
+---
+summary: "All supported providers (models + messaging) in one place"
+read_when:
+  - You want a single hub for every provider we document
+  - You want model providers vs chat providers split clearly
+---
+# Providers hub
+
+This hub covers **model providers** (LLMs) and **messaging/chat providers** (WhatsApp, Telegram, etc).
+For model selection rules, see [/concepts/models](/concepts/models). For the full provider catalog, see
+[/concepts/model-providers](/concepts/model-providers).
+
+## Model providers
+
+- [OpenAI (API + Codex)](/providers/openai)
+- [Anthropic (API + Claude CLI)](/providers/anthropic)
+- [OpenRouter](/providers/openrouter)
+- [OpenCode Zen](/providers/opencode)
+- [Z.AI](/providers/zai)
+- [GLM models](/providers/glm)
+
+Full list (xAI, Groq, Mistral, etc.): [/concepts/model-providers](/concepts/model-providers)
+
+## Messaging + chat providers
+
+- [WhatsApp](/providers/whatsapp)
+- [Telegram](/providers/telegram)
+- [Telegram (grammY notes)](/providers/grammy)
+- [Slack](/providers/slack)
+- [Discord](/providers/discord)
+- [Signal](/providers/signal)
+- [iMessage](/providers/imessage)
+- [Location parsing](/providers/location)
+- [Provider troubleshooting](/providers/troubleshooting)
+
+## Ingress + web
+
+- [WebChat](/web/webchat)
+- [Webhooks](/automation/webhook)
+- [Gmail Pub/Sub](/automation/gmail-pubsub)