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

docs/configuration-guide.md

@@ -49,14 +49,25 @@ Based on our experience developing LEANN, embedding models fall into three categ
 - **Cons**: Slower inference, longer index build times
 - **Use when**: Quality is paramount and you have sufficient compute resources. **Highly recommended** for production use
 
-### Quick Start: OpenAI Embeddings (Fastest Setup)
+### Quick Start: Cloud and Local Embedding Options
 
+**OpenAI Embeddings (Fastest Setup)**
 For immediate testing without local model downloads:
 ```bash
 # Set OpenAI embeddings (requires OPENAI_API_KEY)
 --embedding-mode openai --embedding-model text-embedding-3-small
 ```
 
+**Ollama Embeddings (Privacy-Focused)**
+For local embeddings with complete privacy:
+```bash
+# First, pull an embedding model
+ollama pull nomic-embed-text
+
+# Use Ollama embeddings
+--embedding-mode ollama --embedding-model nomic-embed-text
+```
+
 <details>
 <summary><strong>Cloud vs Local Trade-offs</strong></summary>