Add fetch/conversion metrics and improve logging

FetchResult now includes:
- StatusCode: HTTP status from upstream
- FetchDurationMs: time to fetch from upstream
- RemoteAddr: upstream server address

SourceMetadata now stores:
- ContentLength: size from upstream
- FetchDurationMs: fetch timing
- RemoteAddr: for debugging

Image conversion log now includes:
- host: source hostname (was missing)
- path: source path (renamed from file)
- convert_ms: image processing time
- quality: requested quality setting
- fit: requested fit mode

internal/imgcache/fetcher.go

@@ -164,7 +164,12 @@ func (f *HTTPFetcher) Fetch(ctx context.Context, url string) (*FetchResult, erro
 	req.Header.Set("User-Agent", f.config.UserAgent)
 	req.Header.Set("Accept", strings.Join(f.config.AllowedContentTypes, ", "))
 
+	startTime := time.Now()
+
 	resp, err := f.client.Do(req)
+
+	fetchDuration := time.Since(startTime)
+
 	if err != nil {
 		if errors.Is(err, context.DeadlineExceeded) {
 			return nil, ErrUpstreamTimeout
@@ -173,6 +178,12 @@ func (f *HTTPFetcher) Fetch(ctx context.Context, url string) (*FetchResult, erro
 		return nil, fmt.Errorf("upstream request failed: %w", err)
 	}
 
+	// Get remote address if available
+	var remoteAddr string
+	if resp.Request != nil && resp.Request.URL != nil {
+		remoteAddr = resp.Request.Host
+	}
+
 	// Check status code
 	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
 		_ = resp.Body.Close()
@@ -198,10 +209,13 @@ func (f *HTTPFetcher) Fetch(ctx context.Context, url string) (*FetchResult, erro
 	success = true
 
 	return &FetchResult{
-		Content:       &semaphoreReleasingReadCloser{limitedBody, resp.Body, sem},
-		ContentLength: resp.ContentLength,
-		ContentType:   contentType,
-		Headers:       resp.Header,
+		Content:         &semaphoreReleasingReadCloser{limitedBody, resp.Body, sem},
+		ContentLength:   resp.ContentLength,
+		ContentType:     contentType,
+		Headers:         resp.Header,
+		StatusCode:      resp.StatusCode,
+		FetchDurationMs: fetchDuration.Milliseconds(),
+		RemoteAddr:      remoteAddr,
 	}, nil
 }