feat: inversion relation User→Projects, les projets pointent vers les utilisateurs

Le champ `users` est désormais sur le blueprint projet. Les blueprints
pochet/client perdent leur champ `projects`. La logique PHP (user-projects,
managers, controller, template, mark-all-read) lit project.users au lieu
de user.projects. Script de migration inclus.

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

public/site/config/routes/migrate-user-projects.php

@@ -0,0 +1,75 @@
+<?php
+
+/**
+ * Script de migration : inverse la relation User→Projects en Project→Users.
+ *
+ * Pour chaque user (non-admin) ayant un champ projects non vide,
+ * ajoute ce user dans le champ `users` du projet correspondant.
+ *
+ * Idempotent : pas de doublons si exécuté plusieurs fois.
+ * À supprimer après migration.
+ *
+ * Usage: POST /migrate-user-projects.json
+ */
+
+return [
+  'pattern' => 'migrate-user-projects.json',
+  'method' => 'POST',
+  'action' => function () {
+    $user = kirby()->user();
+
+    if (!$user || $user->role()->id() !== 'admin') {
+      return [
+        'status' => 'error',
+        'message' => 'Cette action nécessite les droits administrateur.'
+      ];
+    }
+
+    $migrated = [];
+    $errors = [];
+
+    $nonAdminUsers = kirby()->users()->filter(fn($u) => $u->role()->id() !== 'admin');
+
+    foreach ($nonAdminUsers as $u) {
+      if (!$u->projects()->exists() || $u->projects()->isEmpty()) {
+        continue;
+      }
+
+      $userProjects = $u->projects()->toPages();
+
+      foreach ($userProjects as $project) {
+        try {
+          $currentUsers = $project->users()->yaml();
+
+          $userUuid = $u->uuid()->toString();
+
+          if (in_array($userUuid, $currentUsers)) {
+            continue;
+          }
+
+          $currentUsers[] = $userUuid;
+          $project->update(['users' => $currentUsers]);
+
+          $migrated[] = [
+            'user' => $u->name()->value(),
+            'email' => $u->email(),
+            'project' => $project->title()->value(),
+          ];
+        } catch (\Throwable $th) {
+          $errors[] = [
+            'user' => $u->email(),
+            'project' => $project->title()->value(),
+            'error' => $th->getMessage()
+          ];
+        }
+      }
+    }
+
+    return [
+      'status' => 'success',
+      'message' => count($migrated) . ' assignations migrées.',
+      'migrated' => $migrated,
+      'errors' => $errors
+    ];
+  }
+];