fix: Add .huggingfaceignore to prevent TSV/schema conflicts

- Prevents auto-detection of .tsv files that have different column names
- Ensures only .jsonl files are used for dataset loading
- Resolves CastError when loading from Hugging Face Hub

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

.huggingfaceignore

@@ -0,0 +1,6 @@
+# Ignore .tsv annotation files to prevent schema conflicts
+# The dataset should only load the .jsonl files by default
+*.tsv
+train/
+val/
+test/