Replace awesome_nested_set with a plain parent_id-based NestedTree concern

Root-caused this session: appending a child to any node never widened
that parent's own rgt boundary, on the pinned revision (Gemfile tracked
main directly, chasing a too-conservative gemspec constraint - not, as
first assumed, a deliberate pin to avoid a known bug). Reproduced
cleanly on a single ordinary create with no concurrency and no bulk
operation involved, confirmed via the gem's own SetValidator, then
confirmed as the root cause of nodes_controller_test.rb's 3 long-standing
"pre-existing" failures - not three separate mysteries, one bug.

admin_controller's sitemap needed its own real conversion, not just a
drop-in: awesome_nested_set's lft column implicitly provided correct
depth-first tree order for free, which the old code combined with a
separate class-level each_with_level iterator. Both replaced by one
method, self_and_descendants_ordered_with_level, computing an ordered
[node, level] list in a single query-then-walk pass - checked against
the actual view template first (admin/index.html.erb) rather than
assumed, since it relies on list order alone to render correct visual
nesting.

lft/rgt/depth columns intentionally left in schema, unused - dropping
them is a separate, deliberately deferred migration once this is proven
running for a while, not bundled with the behavior change.

1 files changed, 3 insertions, 5 deletions

diff --git a/app/controllers/admin_controller.rb b/app/controllers/admin_controller.rb
index bfc6cd8..3fa0519 100644
--- a/app/controllers/admin_controller.rb
+++ b/app/controllers/admin_controller.rb
@@ -15,12 +15,10 @@ class AdminController < ApplicationController
       Time.now, Time.now - 14.days
     ).limit(50).order("updated_at desc")
 
-    all_nodes = Node.root.self_and_descendants
+    ordered_with_level = Node.root.self_and_descendants_ordered_with_level
     @sitemap_depth = {}
-    Node.each_with_level(all_nodes) do |node, level|
-      @sitemap_depth[node.id] = level
-    end
-    @sitemap = all_nodes.to_a.sort! { |node1,node2| node1.lft <=> node2.lft }.delete_if { |node| node.update? }
+    ordered_with_level.each { |node, level| @sitemap_depth[node.id] = level }
+    @sitemap = ordered_with_level.map(&:first).reject(&:update?)
 
     @mypages = Page.where("user_id = ? or editor_id = ?", @current_user, @current_user)