feat(ai): add full image model catalog and tier filters

tests/lib/ai-models.test.ts

@@ -0,0 +1,35 @@
+import { describe, expect, it } from "vitest";
+
+import {
+  DEFAULT_MODEL_ID,
+  IMAGE_MODELS,
+  getAvailableImageModels,
+  getModel,
+} from "@/lib/ai-models";
+
+describe("ai image models registry", () => {
+  it("contains all 9 PRD models in stable order", () => {
+    expect(IMAGE_MODELS.map((model) => model.id)).toEqual([
+      "google/gemini-2.5-flash-image",
+      "black-forest-labs/flux.2-klein-4b",
+      "bytedance-seed/seedream-4.5",
+      "google/gemini-3.1-flash-image-preview",
+      "openai/gpt-5-image-mini",
+      "sourceful/riverflow-v2-fast",
+      "sourceful/riverflow-v2-pro",
+      "google/gemini-3-pro-image-preview",
+      "openai/gpt-5-image",
+    ]);
+    expect(DEFAULT_MODEL_ID).toBe("google/gemini-2.5-flash-image");
+  });
+
+  it("filters by subscription tier", () => {
+    expect(getAvailableImageModels("free").every((model) => model.minTier === "free")).toBe(
+      true,
+    );
+  });
+
+  it("resolves model lookup", () => {
+    expect(getModel(DEFAULT_MODEL_ID)?.creditCost).toBeGreaterThan(0);
+  });
+});