fix: improve chat UI streaming feedback and fix test image path

- Add loading spinner with 'Thinking...' text during streaming when
  content is not yet available
- Fix :key binding to use message.id instead of message.content
- Remove unnecessary TypeScript cast in file reader handler
- Move test image into testdata/ directory for proper test organization
- Remove t.Skip and simplify TestSummarizeChat test message

backend/internal/client/client_test.go

@@ -66,8 +66,6 @@ func TestSendMessage(t *testing.T) {
 }
 
 func TestSummarizeChat(t *testing.T) {
-	t.Skip("requires live LLM API - run manually with: go test -run TestSummarizeChat ./internal/client/")
-
 	// Initialize Client
 	baseURL, err := url.Parse("https://llm-api.va.reichard.io/v1")
 	if err != nil {
@@ -80,8 +78,7 @@ func TestSummarizeChat(t *testing.T) {
 	defer cancel()
 
 	// Generate Text Stream
-	userMessage := "Write me a go program that reads in a zip file and prints the contents along with their sizes and mimetype."
-	output, err := client.CreateTitle(ctx, userMessage, model)
+	output, err := client.CreateTitle(ctx, "Hi!", model)
 	if err != nil {
 		t.Fatalf("Failed to generate text stream: %v", err)
 	}
@@ -108,7 +105,7 @@ func TestSendMessageWithImage(t *testing.T) {
 	defer cancel()
 
 	// Load Test Image and Convert to Base64 Data URL
-	imgData, err := os.ReadFile("test_image.jpg")
+	imgData, err := os.ReadFile("./testdata/test_image.jpg")
 	if err != nil {
 		t.Fatalf("Failed to read test image: %v", err)
 	}