ollama build more customizable

[seun-ja]

Makes Ollama build more configurable, can get base_url via env

[Copilot]

Pull request overview

This PR makes the Ollama provider client configuration more flexible by allowing the Ollama API base URL to be configured via an environment variable, rather than always using the default client settings.

Changes:

• Switch Ollama client initialization to use Client::builder() instead of Client::new(...).
• Read OLLAMA_API_BASE_URL from the environment with a localhost default.

---

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[Copilot]

std::env::var(...).unwrap_or("http://localhost:11434".to_string()) eagerly allocates the default String even when the env var is set. Prefer unwrap_or_else (or a const/Cow) so the default allocation only happens on the error path.

Suggested change

	let base_url =
	std::env::var("OLLAMA_API_BASE_URL").unwrap_or("http://localhost:11434".to_string());
	let base_url = std::env::var("OLLAMA_API_BASE_URL")
	.unwrap_or_else(|_| "http://localhost:11434".to_string());

[Copilot]

std::env::var("OLLAMA_API_BASE_URL").unwrap_or(...) falls back to localhost for any VarError, including NotUnicode. That can silently ignore a misconfigured env var and be hard to diagnose. Consider only defaulting on VarError::NotPresent and returning an error for other cases.

Suggested change

	let base_url =
	std::env::var("OLLAMA_API_BASE_URL").unwrap_or("http://localhost:11434".to_string());
	let base_url = match std::env::var("OLLAMA_API_BASE_URL") {
	Ok(base_url) => base_url,
	Err(std::env::VarError::NotPresent) => "http://localhost:11434".to_string(),
	Err(err) => return Err(err.into()),
	};