fix: clippy warnings (for_kv_map, saturating_sub)

Author: omoshola-o

src/mcp/server.rs

@@ -3670,7 +3670,7 @@ impl McpServer {
         let mut by_lang: HashMap<String, usize> = HashMap::new();
         let mut by_type: HashMap<String, usize> = HashMap::new();
         let mut total = 0usize;
-        for (_gn, graph) in &self.graphs {
+        for graph in self.graphs.values() {
             for unit in graph.units() {
                 if !languages.is_empty()
                     && !languages

src/temporal/archaeology.rs

@@ -195,7 +195,7 @@ impl<'g> CodeArchaeologist<'g> {
 
         let oldest = self.history.oldest_timestamp(&unit.file_path);
         let latest = self.history.latest_timestamp(&unit.file_path);
-        let age_seconds = if latest > oldest { latest - oldest } else { 0 };
+        let age_seconds = latest.saturating_sub(oldest);
 
         // Infer evolution phase
         let phase = self.infer_phase(