feat: prefer base64 inline image for summary, fall back to S3

Send the screenshot to the multimodal model inline as a base64 data URL
so summarisation no longer requires S3 to be configured or publicly
reachable. Only when the PNG exceeds the provider MaxInlineBytes limit
do we upload to S3, verify the public URL is reachable, and delete the
temporary object once done. Oversized images without S3 now surface a
clear hint instead of a hard S3 requirement.

internal/application/capture_summary_test.go

@@ -2,6 +2,7 @@ package application
 
 import (
 	"context"
+	"strings"
 	"testing"
 )
 
@@ -10,6 +11,7 @@ type fakeOSSProvider struct {
 	data        []byte
 	contentType string
 	url         string
+	deletedKey  string
 }
 
 func (f *fakeOSSProvider) Upload(_ context.Context, key string, data []byte, contentType string) (string, error) {
@@ -24,6 +26,11 @@ func (f *fakeOSSProvider) Upload(_ context.Context, key string, data []byte, con
 
 func (f *fakeOSSProvider) Name() string { return "fake" }
 
+func (f *fakeOSSProvider) Delete(_ context.Context, key string) error {
+	f.deletedKey = key
+	return nil
+}
+
 type fakeSummarizer struct {
 	prompt string
 	url    string
@@ -84,3 +91,50 @@ func TestCaptureSummaryServiceUploadsSummarizesAndCopies(t *testing.T) {
 		t.Fatalf("expected summary copied, got %q", clip.text)
 	}
 }
+
+func TestCaptureSummaryServiceInlineDataURL(t *testing.T) {
+	svc := &CaptureSummaryService{MaxInlineBytes: 10}
+
+	if !svc.CanInline([]byte("small")) {
+		t.Fatalf("expected 5-byte payload to be inlinable under 10-byte cap")
+	}
+	if svc.CanInline([]byte("this is definitely too big")) {
+		t.Fatalf("expected oversized payload to be rejected for inlining")
+	}
+
+	url := svc.InlineDataURL([]byte("png"))
+	if !strings.HasPrefix(url, "data:image/png;base64,") {
+		t.Fatalf("expected base64 data URL prefix, got %q", url)
+	}
+	if strings.Contains(url, "https://") {
+		t.Fatalf("inline URL must not be a remote URL, got %q", url)
+	}
+}
+
+func TestCaptureSummaryServiceDeleteUploadedUsesDeleter(t *testing.T) {
+	provider := &fakeOSSProvider{}
+	svc := &CaptureSummaryService{Provider: provider}
+
+	if err := svc.DeleteUploaded(context.Background(), "snapgo/a.png"); err != nil {
+		t.Fatalf("delete uploaded: %v", err)
+	}
+	if provider.deletedKey != "snapgo/a.png" {
+		t.Fatalf("expected object deleted, got %q", provider.deletedKey)
+	}
+}
+
+func TestCaptureSummaryServiceDeleteUploadedNoDeleterIsNoop(t *testing.T) {
+	// A provider without Delete must not error when cleanup is requested.
+	svc := &CaptureSummaryService{Provider: nonDeletingProvider{}}
+	if err := svc.DeleteUploaded(context.Background(), "snapgo/a.png"); err != nil {
+		t.Fatalf("expected no-op delete, got %v", err)
+	}
+}
+
+type nonDeletingProvider struct{}
+
+func (nonDeletingProvider) Upload(_ context.Context, _ string, _ []byte, _ string) (string, error) {
+	return "https://cdn.example.com/x.png", nil
+}
+
+func (nonDeletingProvider) Name() string { return "no-delete" }