feat: Gemini image generation test button in admin settings

API: new testGeminiConnection adminProcedure
- Generates a simple test image via Gemini API
- Returns { ok, model } on success, { ok: false, error } on failure
- Audit logged: "Gemini test succeeded/failed"

UI: "Test Gemini" button next to "Save Image Settings"
- Only visible when Gemini provider is selected
- Shows green success or red error result below the buttons
- Displays the model name on success

Model: gemini-2.0-flash-preview-image-generation (correct name)

Co-Authored-By: claude-flow <ruv@ruv.net>

packages/api/src/router/settings.ts

@@ -319,6 +319,48 @@ export const settingsRouter = createTRPCRouter({
     return result;
   }),
 
+  testGeminiConnection: adminProcedure.mutation(async ({ ctx }) => {
+    const settings = await ctx.db.systemSettings.findUnique({
+      where: { id: "singleton" },
+      select: { geminiApiKey: true, geminiModel: true },
+    });
+
+    if (!settings?.geminiApiKey) {
+      return { ok: false, error: "Gemini API key is not configured." };
+    }
+
+    try {
+      const { generateGeminiImage } = await import("../gemini-client.js");
+      const model = settings.geminiModel ?? "gemini-2.0-flash-preview-image-generation";
+
+      // Generate a tiny test image with a simple prompt
+      const dataUrl = await generateGeminiImage(
+        settings.geminiApiKey,
+        "A simple blue circle on white background, minimal, 256x256",
+        model,
+      );
+
+      const hasImage = dataUrl.startsWith("data:image/");
+
+      void createAuditEntry({
+        db: ctx.db,
+        entityType: "SystemSettings",
+        entityId: "singleton",
+        entityName: "Gemini Connection Test",
+        action: "UPDATE",
+        userId: ctx.dbUser?.id,
+        after: { testResult: hasImage ? "success" : "failed" },
+        source: "ui",
+        summary: hasImage ? "Gemini image generation test succeeded" : "Gemini test returned no image",
+      });
+
+      return { ok: hasImage, model, preview: hasImage ? dataUrl.slice(0, 100) + "..." : undefined };
+    } catch (err) {
+      const { parseGeminiError } = await import("../gemini-client.js");
+      return { ok: false, error: parseGeminiError(err) };
+    }
+  }),
+
   getAiConfigured: protectedProcedure.query(async ({ ctx }) => {
     const settings = await ctx.db.systemSettings.findUnique({
       where: { id: "singleton" },