chore: switch to DeepSeek API + sentence-transformers for free deployment

- Replace OpenAI LLM with DeepSeek (deepseek-chat) via OpenAI-compatible client
- Replace OpenAI embeddings with local sentence-transformers (all-MiniLM-L6-v2)
- Pre-download embedding model during Docker build
- Add .gitignore

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -10,6 +10,9 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 COPY requirements.txt .
 RUN pip install --no-cache-dir -r requirements.txt
 
+# Pre-download embedding model agar tidak diunduh ulang saat runtime
+RUN python -c "from sentence_transformers import SentenceTransformer; SentenceTransformer('all-MiniLM-L6-v2')"
+
 COPY src/ ./src/
 
 CMD ["python", "src/main.py"]