Add embed endpoint (POST /api/embed)

Implement the Ollama POST /api/embed endpoint for generating vector
embeddings from text input.

- Add EmbedInput, EmbedRequest, EmbedResponse types in src/types/embed.rs
- Add OllamaClient::embed() async method in src/lib.rs
- Register embed module in src/types/mod.rs
- Add usage example in examples/embed.rs
- Update README with embed endpoint documentation

examples/embed.rs

@@ -0,0 +1,24 @@
+use std::{env, error::Error};
+
+use ollama_rs::OllamaClient;
+use ollama_rs::types::embed::EmbedRequest;
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn Error>> {
+    tracing_subscriber::fmt().init();
+    let _ = dotenvy::dotenv();
+    let server_address = env::var("OLLAMA_SERVER")?;
+    let ollama_client = OllamaClient::new(server_address);
+    let request = EmbedRequest::builder("embeddinggemma")
+        .input("Generate embeddings for this text")
+        .build();
+
+    let response = ollama_client.embed(request).await?;
+    for (i, embedding) in response.embeddings.iter().enumerate() {
+        println!("Embedding {}: {} dimensions", i, embedding.len());
+        if embedding.len() >= 3 {
+            println!("  First 3 values: {:?}", &embedding[..3]);
+        }
+    }
+    Ok(())
+}