feat(gemini): fetch URL images as inlineData for multimodal prompts

src/models/gemini.test.ts

@@ -164,6 +164,47 @@ describe('GeminiClient', () => {
     expect(response.stopReason).toBe('max_tokens');
   });
 
+  it('fetches URL image content and sends inlineData parts', async () => {
+    const fetchMock = vi.fn().mockResolvedValue({
+      ok: true,
+      headers: { get: (name: string) => name.toLowerCase() === 'content-type' ? 'image/png' : null },
+      arrayBuffer: async () => Uint8Array.from([1, 2, 3, 4]).buffer,
+    } as unknown as Response);
+    vi.stubGlobal('fetch', fetchMock);
+
+    const client = new GeminiClient({
+      apiKey: 'test-key',
+      model: 'gemini-2.0-flash',
+    });
+
+    await client.chat({
+      messages: [{
+        role: 'user',
+        content: [
+          { type: 'text', text: 'describe this image' },
+          { type: 'image', source: { type: 'url', url: 'https://example.com/test.png', media_type: 'image/png' } },
+        ],
+      }],
+    });
+
+    expect(fetchMock).toHaveBeenCalledWith('https://example.com/test.png');
+    expect(mockGenerateContent).toHaveBeenCalledWith({
+      contents: [{
+        role: 'user',
+        parts: [
+          { text: 'describe this image' },
+          {
+            inlineData: {
+              mimeType: 'image/png',
+              data: Buffer.from([1, 2, 3, 4]).toString('base64'),
+            },
+          },
+        ],
+      }],
+    });
+    vi.unstubAllGlobals();
+  });
+
   it('uses environment variable for API key when not provided', () => {
     const originalEnv = process.env.GOOGLE_API_KEY;
     process.env.GOOGLE_API_KEY = 'env-key';