connectivity: suggest link-add commands for islands

When connectivity shows isolated nodes, print copy-pasteable
poc-memory graph link-add commands targeting the highest-degree
node in the largest cluster. Closes the diagnose→fix loop.

poc-memory/src/query.rs

@@ -579,9 +579,20 @@ fn print_connectivity(results: &[QueryResult], graph: &Graph) {
 
     let result_set: std::collections::HashSet<&str> = keys.iter().copied().collect();
 
+    // Find the largest cluster to use as link-add target for islands
+    let largest_cluster = components.iter()
+        .max_by_key(|c| c.len())
+        .and_then(|c| if c.len() > 1 {
+            // Pick highest-degree node in largest cluster as link target
+            c.iter().max_by_key(|k| graph.degree(k)).cloned()
+        } else { None });
+
+    let mut islands: Vec<&str> = Vec::new();
+
     for (i, component) in components.iter().enumerate() {
         if component.len() == 1 {
             println!("  island: {}", component[0]);
+            islands.push(&component[0]);
         } else {
             println!("  cluster {} ({} nodes):", i + 1, component.len());
             for node in component {
@@ -604,4 +615,14 @@ fn print_connectivity(results: &[QueryResult], graph: &Graph) {
             }
         }
     }
+
+    // Suggest link-add commands for islands
+    if !islands.is_empty() {
+        if let Some(ref hub) = largest_cluster {
+            println!("\nFix islands:");
+            for island in &islands {
+                println!("  poc-memory graph link-add {} {}", island, hub);
+            }
+        }
+    }
 }