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).

src/bin/memory-search.rs

@@ -12,6 +12,7 @@ use std::fs;
 use std::io::{self, Read, Write};
 use std::path::{Path, PathBuf};
 use std::process::Command;
+use std::time::{Duration, SystemTime};
 
 fn main() {
     let mut input = String::new();
@@ -66,6 +67,9 @@ fn main() {
     let state_dir = PathBuf::from("/tmp/claude-memory-search");
     fs::create_dir_all(&state_dir).ok();
 
+    // Clean up state files older than 24h (opportunistic, best-effort)
+    cleanup_stale_files(&state_dir, Duration::from_secs(86400));
+
     let cookie = load_or_create_cookie(&state_dir, session_id);
     let seen = load_seen(&state_dir, session_id);
 
@@ -172,3 +176,20 @@ fn mark_seen(dir: &Path, session_id: &str, key: &str) {
         writeln!(f, "{}", key).ok();
     }
 }
+
+fn cleanup_stale_files(dir: &Path, max_age: Duration) {
+    let entries = match fs::read_dir(dir) {
+        Ok(e) => e,
+        Err(_) => return,
+    };
+    let cutoff = SystemTime::now() - max_age;
+    for entry in entries.flatten() {
+        if let Ok(meta) = entry.metadata() {
+            if let Ok(modified) = meta.modified() {
+                if modified < cutoff {
+                    fs::remove_file(entry.path()).ok();
+                }
+            }
+        }
+    }
+}