Add OpenAI-compatible model client

internal/llm/client.go

@@ -0,0 +1,11 @@
+package llm
+
+import (
+	"context"
+	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
+)
+
+// Client executes a rendered prompt against an LLM endpoint.
+type Client interface {
+	Generate(ctx context.Context, req domain.GenerateRequest) (*domain.GenerateResponse, error)
+}