spectral decomposition, search improvements, char boundary fix

- New spectral module: Laplacian eigendecomposition of the memory graph.
  Commands: spectral, spectral-save, spectral-neighbors, spectral-positions,
  spectral-suggest. Spectral neighbors expand search results beyond keyword
  matching to structural proximity.

- Search: use StoreView trait to avoid 6MB state.bin rewrite on every query.
  Append-only retrieval logging. Spectral expansion shows structurally
  nearby nodes after text results.

- Fix panic in journal-tail: string truncation at byte 67 could land inside
  a multi-byte character (em dash). Now walks back to char boundary.

- Replay queue: show classification and spectral outlier score.

- Knowledge agents: extractor, challenger, connector prompts and runner
  scripts for automated graph enrichment.

- memory-search hook: stale state file cleanup (24h expiry).

Cargo.toml

@@ -11,6 +11,9 @@ serde_json = "1"
 bincode = "1"
 regex = "1"
 libc = "0.2"
+faer = "0.24.0"
+rkyv = { version = "0.7", features = ["validation", "std"] }
+memmap2 = "0.9"
 
 [build-dependencies]
 capnpc = "0.20"