Delete similarity module, rewrite module, and all text-similarity code

Text cosine similarity was being used as a crutch for operations
the graph structure should handle: interference detection, orphan
linking, triangle closing, hub differentiation. These are all
graph-structural operations that the agents (linker, extractor)
handle with actual semantic understanding.

Removed: similarity.rs (stemming + cosine), rewrite.rs (orphan
linking, triangle closing, hub differentiation), detect_interference,
and all CLI commands and consolidation steps that used them.

-794 lines.

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/hippocampus/mod.rs

@@ -11,7 +11,6 @@ pub mod graph;
 pub mod lookups;
 pub mod cursor;
 pub mod query;
-pub mod similarity;
 pub mod spectral;
 pub mod neuro;
 pub mod counters;