Initial Drupal site: content model + validation + Vue dashboard

- Content type "Ligne comptable" with Paragraphs "Répartition" (Compte + Montant)
- Taxonomies: Compte (9 comptes) and Client (unified client list)
- hook_node_presave + form validate: sum(répartition) must equal montant HT
- /dashboard route (progressive decoupling): Vue 3 app fetching JSON:API,
  computing solde par compte / par client client-side
- "Ajouter une ligne" opens the real Drupal node form in an AJAX modal
- Gin as default + admin theme
- 9 opening-balance lines seeded from suivi_compta_SASFigli2026_v2.ods

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

web/themes/README.txt

@@ -0,0 +1,31 @@
+Themes allow you to change the look and feel of your Drupal site. You can use
+themes contributed by others or create your own.
+
+WHAT TO PLACE IN THIS DIRECTORY?
+--------------------------------
+
+Placing downloaded and custom themes in this directory separates downloaded and
+custom themes from Drupal core's themes. This allows Drupal core to be updated
+without overwriting these files.
+
+DOWNLOAD ADDITIONAL THEMES
+--------------------------
+
+Contributed themes from the Drupal community may be downloaded at
+https://www.drupal.org/project/project_theme.
+
+MULTISITE CONFIGURATION
+-----------------------
+
+In multisite configurations, themes found in this directory are available to
+all sites. You may also put themes in the sites/all/themes directory, and the
+versions in sites/all/themes will take precedence over versions of the same
+themes that are here. Alternatively, the sites/your_site_name/themes directory
+pattern may be used to restrict themes to a specific site instance.
+
+MORE INFORMATION
+-----------------
+
+Refer to the "Appearance" section of the README.md in the Drupal root directory
+for further information on customizing the appearance of Drupal with custom
+themes.