Security: Add env-example.txt with placeholder token

- Add back env-example.txt with placeholder instead of real token
- File was removed from history to eliminate security risk

env-example.txt

@@ -0,0 +1,4 @@
+# Hugging Face Authentication
+# Get your token from: https://huggingface.co/settings/tokens
+# Required for accessing gated models or to avoid rate limits
+HF_TOKEN=your_hugging_face_token_here