feat(devgen/providers): add OllamaProvider for local Ollama integration

Add a new provider that wraps the local Ollama server using an OpenAI‑compatible client, enabling generation via `ollama_host` configuration. This introduces the first provider for local LLM inference.

New Features
- Implement OllamaProvider with a `generate()` method, supporting custom host, model selection, and robust error handling.

devgen/providers/ollama.py

@@ -0,0 +1,51 @@
+
+
+class OllamaProvider:
+    """Generates content using a local Ollama server.
+
+    Ollama exposes an OpenAI-compatible endpoint at /v1/chat/completions,
+    so we can reuse the openai client. The host defaults to
+    http://localhost:11434 but can be overridden via the
+    `ollama_host` kwarg (or `ollama_host` in ~/.devgen.yaml).
+    """
+
+    DEFAULT_HOST = "http://localhost:11434"
+    DEFAULT_MODEL = "llama3.2"
+
+    def generate(
+        self,
+        prompt: str,
+        api_key: str | None = None,
+        model: str | None = None,
+        **kwargs,
+    ) -> str:
+        from openai import OpenAI
+
+        host = kwargs.get("ollama_host") or self.DEFAULT_HOST
+        base_url = f"{host.rstrip('/')}/v1"
+        chosen_model = model or self.DEFAULT_MODEL
+
+        client = OpenAI(base_url=base_url, api_key=api_key or "ollama")
+
+        kwargs.pop("debug", None)
+        kwargs.pop("ollama_host", None)
+
+        try:
+            response = client.chat.completions.create(
+                model=chosen_model,
+                messages=[{"role": "user", "content": prompt}],
+                **kwargs,
+            )
+        except Exception as e:
+            raise RuntimeError(
+                f"Ollama request failed (host={host}, model={chosen_model}): {e}. "
+                "Is the Ollama server running? Start it with `ollama serve` and "
+                "pull a model with `ollama pull <model>`."
+            ) from e
+
+        if not response.choices:
+            raise RuntimeError(
+                f"Ollama returned no choices for model {chosen_model!r}. "
+                "The model may not be installed locally."
+            )
+        return response.choices[0].message.content.strip()