fix: add updater API response logging to diagnose update check failures

Logs the raw API response body and status from Gitea package API,
plus parsed version count and current version comparison. This will
show exactly why updates aren't being detected.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/updater/service.go

@@ -98,15 +98,24 @@ func (u *UpdateService) CheckForUpdate() (*UpdateInfo, error) {
 	}
 	defer resp.Body.Close()
 
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, fmt.Errorf("read package API response: %w", err)
+	}
+
+	slog.Info("package API response", "status", resp.StatusCode, "body", string(body)[:min(len(body), 500)])
+
 	if resp.StatusCode != http.StatusOK {
-		return nil, fmt.Errorf("unexpected status %d from package API", resp.StatusCode)
+		return nil, fmt.Errorf("unexpected status %d from package API: %s", resp.StatusCode, string(body))
 	}
 
 	var versions []giteaPackageVersion
-	if err := json.NewDecoder(resp.Body).Decode(&versions); err != nil {
+	if err := json.Unmarshal(body, &versions); err != nil {
 		return nil, fmt.Errorf("decode package versions: %w", err)
 	}
 
+	slog.Info("parsed versions", "count", len(versions), "currentVersion", u.currentVersion)
+
 	if len(versions) == 0 {
 		slog.Info("no package versions found")
 		return info, nil