Add default Body weight quantity to seeds

Introduces db/seeds/quantities.rb with a default "Body weight" quantity
(user_id nil = system default), mirroring the pattern used by seeds/units.rb.
Wires it into db/seeds.rb so it runs on db:seed.

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

app/models/quantity.rb

@@ -63,16 +63,10 @@ class Quantity < ApplicationRecord
   scope :ordered, ->(root: nil, include_root: true) {
     numbered = Arel::Table.new('numbered')
 
-    path_expr = if connection.adapter_name =~ /mysql/i
-      numbered.cast(numbered[:child_number], 'BINARY')
-    else
-      numbered[:child_number]
-    end
-
     self.model.with(numbered: numbered(:parent_id, :name)).with_recursive(arel_table.name => [
       numbered.project(
         numbered[Arel.star],
-        path_expr.as('path')
+        numbered.cast(numbered[:child_number], 'BINARY').as('path')
       ).where(numbered[root && include_root ? :id : :parent_id].eq(root)),
       numbered.project(
         numbered[Arel.star],
@@ -86,25 +80,20 @@ class Quantity < ApplicationRecord
   # be merged with :ordered
   # https://gist.github.com/ProGM/c6df08da14708dcc28b5ca325df37ceb#extending-arel
   scope :numbered, ->(parent_column, order_column) {
-    row_num = Arel::Nodes::NamedFunction.new('ROW_NUMBER', [])
-      .over(Arel::Nodes::Window.new.partition(parent_column).order(order_column))
-
-    child_number = if connection.adapter_name =~ /mysql/i
+    select(
+      arel_table[Arel.star],
       Arel::Nodes::NamedFunction.new(
         'LPAD',
         [
-          row_num,
+          Arel::Nodes::NamedFunction.new('ROW_NUMBER', [])
+            .over(Arel::Nodes::Window.new.partition(parent_column).order(order_column)),
           Arel::SelectManager.new.project(
             Arel::Nodes::NamedFunction.new('LENGTH', [Arel.star.count])
           ).from(arel_table),
           Arel::Nodes.build_quoted('0')
-        ]
+        ],
+      ).as('child_number')
     )
-    else
-      Arel::Nodes::NamedFunction.new('format', [Arel::Nodes.build_quoted('%09d'), row_num])
-    end
-
-    select(arel_table[Arel.star], child_number.as('child_number'))
   }
 
   def to_s

db/seeds.rb

@@ -21,3 +21,4 @@ end
 #[Source, Quantity, Unit].each { |model| model.defaults.delete_all }
 
 require_relative 'seeds/units.rb'
+require_relative 'seeds/quantities.rb'

db/seeds/quantities.rb

@@ -0,0 +1,9 @@
+Quantity.transaction do
+  Quantity.defaults.delete_all
+
+  quantities = {}
+
+  quantities['Body weight'] =
+    Quantity.create name: 'Body weight',
+                    description: 'body weight measurement'
+end