v0.4.0 - Semantic Search with FastEmbed

Added

Semantic Search with FastEmbed

• Integrated fastembed-rb for high-quality local embeddings
  • Uses BAAI/bge-small-en-v1.5 model (384-dim, ~67MB ONNX, runs locally)
  • No API key required -- model downloaded once to ~/.cache/fastembed/
  • Asymmetric query/passage encoding for better retrieval accuracy
• FastembedAdapter class implementing the existing Generator interface for drop-in replacement
• Benchmark retrieval scores jumped significantly with real embeddings:
  • Semantic easy: Recall@5 = 0.900, medium: 0.696
  • Hybrid aggregate: Recall@5 = 0.727 (was 0.266 with TF-IDF fallback)

Documentation

• Updated benchmark results throughout README, spec/benchmarks/README, and architecture docs
• Replaced TF-IDF embedding references with FastEmbed in architecture documentation