major: Implement 3-tiered testing architecture

see [docs/testing.md](./docs/testing.md)

tests/evals/google-genai.eval.ts

@@ -0,0 +1,31 @@
+import { describe, test, expect } from "vitest";
+import { z } from "zod";
+import { GeminiProvider } from "../../packages/llm/src/providers/google-genai.js";
+import { llmConfig } from "../../packages/llm/src/config.js";
+
+describe("GeminiProvider Eval", () => {
+  test("structured JSON response against live API", async () => {
+    expect(llmConfig.GOOGLE_API_KEY).toBeDefined();
+    const provider = new GeminiProvider(llmConfig.GOOGLE_API_KEY);
+
+    const ToneSchema = z.object({
+      tone: z.enum(["positive", "negative", "neutral"]),
+      confidence: z.number().min(0).max(1),
+      explanation: z.string().min(1),
+    });
+
+    const response = await provider.generateStructuredResponse({
+      systemPrompt: "You are a helpful assistant. Classify the tone of the user's sentence.",
+      userContext: "I absolutely love this new engine, it works perfectly!",
+      schema: ToneSchema,
+    });
+
+    expect(response.success).toBe(true);
+    expect(response.data).toBeDefined();
+    
+    const data = response.data!;
+    expect(data.tone).toBe("positive");
+    expect(data.confidence).toBeGreaterThan(0.8);
+    expect(data.explanation.length).toBeGreaterThan(0);
+  });
+});