Add Ollama embedding support to enable local embedding models (#22)

* feat: Add Ollama embedding support for local embedding models

* docs: Add clear documentation for Ollama embedding usage

* feat: Enhance Ollama embedding with better error handling and concurrent processing

- Add intelligent model validation and suggestions (inspired by OllamaChat)
- Implement concurrent processing for better performance
- Add retry mechanism with timeout handling
- Provide user-friendly error messages with emojis
- Auto-detect and recommend embedding models
- Add text truncation for long texts
- Improve progress bar display logic

* docs: don't mention it in README

packages/leann-backend-diskann/leann_backend_diskann/diskann_embedding_server.py

@@ -261,7 +261,7 @@ if __name__ == "__main__":
         "--embedding-mode",
         type=str,
         default="sentence-transformers",
-        choices=["sentence-transformers", "openai", "mlx"],
+        choices=["sentence-transformers", "openai", "mlx", "ollama"],
         help="Embedding backend mode",
     )
     parser.add_argument(