search: composable algorithm pipeline
Break search into composable stages that chain left-to-right:
each stage takes seeds Vec<(String, f64)> and returns modified seeds.
Available algorithms:
spread — spreading activation through graph edges
spectral — nearest neighbors in spectral embedding
manifold — (placeholder) extrapolation along seed direction
Stages accept inline params: spread,max_hops=4,edge_decay=0.5
memory-search gets --hook, --debug, --seen modes plus positional
pipeline args. poc-memory search gets -p/--pipeline flags.
Also: fix spectral decompose() to skip zero eigenvalues from
disconnected components, filter degenerate zero-coord nodes from
spectral projection, POC_AGENT bail-out for daemon agents, all
debug output to stdout.
Co-Authored-By: ProofOfConcept <poc@bcachefs.org>
c1664bf76b