This release adds support for swappable embedding models with different dimensions.

Features:
- Support for embedding models with 768D, 1024D, 1536D, or 3072D dimensions
- Use any HuggingFace sentence-transformer model
- New FORCE_EMBEDDING_CHANGE_AT_STARTUP option for safe model switching
- New HNSW_EF_SEARCH parameter for tuning recall vs speed
- New download-memories.sh script for memory export

To switch models:
1. Edit recallium.env and set EMBEDDING_MODEL and EMBEDDING_DIM
2. Set FORCE_EMBEDDING_CHANGE_AT_STARTUP=true
3. Restart Recallium (embeddings will be regenerated)

Included model presets:
- Nomic (768D) - Default, ARM64 compatible
- Snowflake Arctic (1024D) - No trust_remote_code needed