docs.rig.rs examples out of sync with rig-core 0.36.0 (from_env Result + cli_chatbot usage)

Hi! I just started experimenting with Rig and ran into a couple docs examples that do not compile for me.

I am using `rig-core = 0.36.0`.

## 1) Quickstart example: `Client::from_env()` result is not handled

Page: `https://docs.rig.rs/docs/quickstart/getting_started`

Current snippet:

```rust
use rig::client::{CompletionClient, ProviderClient};
use rig::completion::Prompt;
use rig::providers::openai;

#[tokio::main]
async fn main() -> Result<(), anyhow::Error> {
// Create OpenAI client
let client = openai::Client::from_env();

// Create agent with a single context prompt
let comedian_agent = client
.agent("gpt-5.2")
.preamble("You are a comedian here to entertain the user using humour and jokes.")
.build();

// Prompt the agent and print the response
let response = comedian_agent.prompt("Entertain me!").await?;

println!("{response}");

Ok(())
}
```

`Client::from_env()` returns `Result`, so this would need a `?` to propagate the error up or explicit error handling.

## 2) CLI chatbot example uses old API shape

Page: `https://docs.rig.rs/docs/extensions/cli_chatbot`

Current snippet:

```rust
use rig::{cli_chatbot, providers::openai};

let agent = openai.agent("gpt-4")
.preamble("You are a helpful assistant.")
.build();

cli_chatbot(agent).await?;
```

To my knowledge, `cli_chatbot` is a module, not a callable function in `rig-core 0.36.0`.
Suggested fix is builder-based:

```rust
use rig::integrations::cli_chatbot::ChatBotBuilder;

// ...
let chatbot = ChatBotBuilder::new().agent(agent).build();
chatbot.run().await?;
```

If this looks right, I’m happy to open a PR with these fixes. Should I go ahead?

The issue points to two specific documentation pages on docs.rig.rs. The first is the quickstart guide where `Client::from_env()` needs error handling. The second is the CLI chatbot extension page where the API usage is outdated. Check the current rig-core 0.36.0 source to confirm the correct API, then update the MDX files in the documentation repository accordingly. Verify the changes by building the docs locally.

索引モデルが issue の本文から書いたものです。