Spectral decomposition (eigenvalue computation) removed — it was
only used by the spectral-save CLI command. The spectral embedding
reader and query engine features remain (they load pre-computed
embeddings from disk, no faer needed).
Removes: faer, nano-gemm, private-gemm, and ~220 other transitive
dependencies. Significant build time and artifact size reduction.
Co-Authored-By: Kent Overstreet <kent.overstreet@linux.dev>