GitHub Streak Stats not loading (broken image)

**Describe the bug**
The GitHub Streak Stats image from `https://github-readme-streak-stats.herokuapp.com` is not loading correctly in my GitHub profile README. Instead of rendering the image, it displays as broken.

**To Reproduce**
Steps to reproduce the behavior:
1. Visit [my profile](https://github.com/DarkSylver)
2. Observe that the image does not load
3. Alternatively, embed the image URL (https://github-readme-streak-stats.herokuapp.com/?user=DarkSylver&theme=tokyonight) in a GitHub profile README and view the broken image icon

**Expected behavior**
The image should render a GitHub streak chart with the selected theme (`tokyonight`) and show activity for the user `DarkSylver`.

**Screenshots**

**Desktop:**
- **Device**: Dell Latitude 3520
- **OS**: Microsoft Windows 10 Pro
- Version: 10.0.19045 Build 19045
- **Browser**: Google Chrome
- Version: 123.0.6312.107

**Smartphone:**
- **Not tested on mobile**

**Network**
- **Connection**: Wired Ethernet (Realtek PCIe GbE)

**Additional context**
Other dynamic content such as language usage stats are loading fine in the same README. This issue seems isolated to the GitHub Streak Stats service, possibly related to Heroku availability or a backend failure.