Display mounts as sublists under their scope header instead of a flat
list with inline scope tags. Each scope header shows the scope name
and config file path (when applicable). Example:

  Volume mounts
    builtin
      ✓ /path/.pi → /root/.pi
    user (~/.config/ramekin/config.kdl)
      ✓ /path/.config/git → /root/.config/git (ro)

diff --git a/src/main.rs b/src/main.rs
index 5d400e4..fe9dd99 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -187,26 +187,29 @@ impl Ramekin {
         if merged.is_empty() {
             println!("  (none)");
         } else {
+            let mut current_scope = None;
             for (scope, m) in &merged {
+                if current_scope != Some(*scope) {
+                    current_scope = Some(*scope);
+                    let label = self
+                        .config
+                        .layers
+                        .iter()
+                        .find(|l| l.scope == *scope)
+                        .and_then(|l| l.path.as_ref())
+                        .map(|p| format!("  {} ({})", scope, p.display()))
+                        .unwrap_or_else(|| format!("  {scope}"));
+                    println!("{label}");
+                }
                 println!(
-                    "  {} {} → {}  ({})",
+                    "    {} {} → {}",
                     check(&m.source),
                     m.source.display(),
-                    m.display_target(),
-                    scope,
+                    m.display_target()
                 );
             }
         }
 
-        println!();
-        println!("Config sources");
-        for layer in &self.config.layers {
-            match layer.path {
-                Some(ref path) => println!("  {} {} {}", check(path), layer.scope, path.display()),
-                None => println!("  ✓ {}", layer.scope),
-            };
-        }
-
         println!();
         println!("Dockerfile");
         match &self.custom_dockerfile {