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/lib.rs

@@ -71,7 +71,7 @@ pub mod channel_capnp {
 // Re-exports — all existing crate::X paths keep working
 pub use hippocampus::{
     store, graph, lookups, cursor, query,
-    similarity, spectral, neuro, counters,
+    spectral, neuro, counters,
     transcript, memory,
 };
 pub use hippocampus::query::engine as search;