Add orcarouter_chat example

orcarouter_chat/.env.example

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+ORCAROUTER_API_KEY=sk-orca-replace-me

orcarouter_chat/.gitignore

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+assets/external/
+.states
+.web
+*.db
+__pycache__/
+*.py[cod]
+.env
+.venv/

orcarouter_chat/README.md

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+# OrcaRouter chat
+
+A minimal Reflex chat app that calls [OrcaRouter](https://www.orcarouter.ai),
+an OpenAI-compatible LLM gateway, and lets you switch between adaptive routing
+(`orcarouter/auto`) and specific upstream models from a dropdown -- same API
+key, same endpoint.
+
+The model dropdown is populated at startup from OrcaRouter's public pricing
+catalog (`https://www.orcarouter.ai/api/pricing`, no auth required), so new
+models added on the server side show up the next time you click **Refresh**.
+If the catalog endpoint is unreachable the app falls back to a curated list of
+flagship models.
+
+## Setup
+
+1. Get an API key at <https://www.orcarouter.ai/console> (the key starts with
+   `sk-orca-`).
+2. Copy the example env file and paste your key:
+   ```bash
+   cp .env.example .env
+   # then edit .env and set ORCAROUTER_API_KEY=sk-orca-...
+   ```
+3. Install dependencies and run:
+   ```bash
+   pip install -r requirements.txt
+   reflex run
+   ```
+
+Open <http://localhost:3000>, pick a model from the dropdown, and start
+chatting.
+
+## What this example demonstrates
+
+- Using OrcaRouter as a drop-in OpenAI-compatible provider
+  (`AsyncOpenAI(base_url="https://api.orcarouter.ai/v1", api_key=...)`).
+- Switching between `orcarouter/auto` (adaptive routing) and specific upstream
+  models (`openai/...`, `anthropic/...`, ...) without changing client code.
+- Passing OrcaRouter-specific routing preferences via the `extra_body` field
+  (`{"models": [...], "route": "fallback"}`).
+- Attaching attribution headers (`HTTP-Referer`, `X-Title`) so OrcaRouter can
+  report which client originated the request.
+- Skipping `temperature` for reasoning models (Claude Opus, GPT-5 family,
+  DeepSeek reasoner) which reject the parameter.
+
+## References
+
+- OrcaRouter docs: <https://docs.orcarouter.ai>
+- Routing strategies and `orcarouter/auto`:
+  <https://www.orcarouter.ai/console/routing>
+- Full model catalog: <https://www.orcarouter.ai/models>