Add admin/editeur/user roles for the associates

root (renamed from the default admin/admin account) keeps full,
unrestricted access outside any role system. These three cover the
actual associates:

- user: read-only, 'access content' only -- can browse /lignes and
  /dashboard, nothing else.
- editeur: 'access content' + create/edit any/delete any
  ligne_comptable content -- can enter and correct accounting lines,
  no site configuration.
- admin: identical permission set to editeur for now (per instruction,
  actual config permissions to be scoped later).

Left the pre-existing "administrator" (is_admin bypass -- too broad)
and "content_editor" (generic Standard-recipe scaffolding, permissions
unrelated to ligne_comptable) roles untouched but unused; worth
pruning later if nothing ends up using them.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

config/sync/user.role.admin.yml

@@ -0,0 +1,18 @@
+uuid: 45d15bb6-7222-481f-8306-58f0d207fa97
+langcode: en
+status: true
+dependencies:
+  config:
+    - node.type.ligne_comptable
+  module:
+    - node
+    - system
+id: admin
+label: Admin
+weight: 6
+is_admin: false
+permissions:
+  - 'access content'
+  - 'create ligne_comptable content'
+  - 'delete any ligne_comptable content'
+  - 'edit any ligne_comptable content'