feat(v2/ollama): scaffold native /api/chat provider

Adds wire types and a Provider struct that will replace the
openaicompat-based Ollama shim with a native /api/chat implementation.
Complete and Stream methods are stubs; subsequent commits implement them.

Adjusts the existing ollama.go to drop the type alias on
openaicompat.Provider (renaming the legacy shim to a temporary internal
helper) so the new native Provider type does not collide. Public New()
still returns the openaicompat-backed provider until Task 4 swaps it.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

v2/ollama/ollama.go

@@ -9,17 +9,28 @@ import (
 	"gitea.stevedudenhoeffer.com/steve/go-llm/v2/openaicompat"
 )
 
-// DefaultBaseURL points at a local Ollama instance with default port.
+// DefaultBaseURL points at a local Ollama instance with default port. Kept
+// for the openaicompat-based shim; callers should migrate to
+// DefaultLocalBaseURL (no /v1 suffix) which targets the native /api/chat
+// endpoint.
 const DefaultBaseURL = "http://localhost:11434/v1"
 
-// Provider is a type alias over openaicompat.Provider.
-type Provider = openaicompat.Provider
-
-// New creates a new Ollama provider. An empty baseURL uses DefaultBaseURL.
-// Ollama ignores the API key; callers may pass "".
-func New(apiKey, baseURL string) *Provider {
+// shimNew is the legacy openaicompat-based constructor, retained until the
+// native provider's Complete/Stream are fully implemented (Task 4 replaces
+// the public New() with a native-backed constructor).
+func shimNew(apiKey, baseURL string) *openaicompat.Provider {
 	if baseURL == "" {
 		baseURL = DefaultBaseURL
 	}
 	return openaicompat.New(apiKey, baseURL, openaicompat.Rules{})
 }
+
+// New creates a new Ollama provider. An empty baseURL uses DefaultBaseURL.
+// Ollama ignores the API key; callers may pass "".
+//
+// Note: this constructor currently still routes through the openaicompat
+// shim. Subsequent commits replace the body with a native /api/chat
+// implementation backed by the Provider type in native.go.
+func New(apiKey, baseURL string) *openaicompat.Provider {
+	return shimNew(apiKey, baseURL)
+}