Extract lib.rs, inline search in memory-search hook

Create lib.rs so all binaries can share library code directly instead
of shelling out to poc-memory. memory-search now calls search::search()
and store::Store::load() in-process instead of Command::new("poc-memory").

The load-context call still shells out (needs get_group_content moved
from main.rs to a library module).

Also: add search::format_results(), deduplicate extract_query_terms.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/search.rs

@@ -139,3 +139,18 @@ pub fn extract_query_terms(text: &str, max_terms: usize) -> String {
         .collect::<Vec<_>>()
         .join(" ")
 }
+
+/// Format search results as text lines (for hook consumption).
+pub fn format_results(results: &[SearchResult]) -> String {
+    let mut out = String::new();
+    for (i, r) in results.iter().enumerate().take(5) {
+        let marker = if r.is_direct { "→" } else { " " };
+        out.push_str(&format!("{}{:2}. [{:.2}/{:.2}] {}",
+            marker, i + 1, r.activation, r.activation, r.key));
+        out.push('\n');
+        if let Some(ref snippet) = r.snippet {
+            out.push_str(&format!("         {}\n", snippet));
+        }
+    }
+    out
+}