fix: correct handler bugs exposed by test suite

- ajustements [numEtud]/[idUE]: fix .where() missing and() — PUT/DELETE
  were applying only numEtud condition, modifying all rows for a student
- modules/users/enseignements POST: add try/catch, return 500 on invalid JSON
- modules/[idModule] PUT: add try/catch + type check on nom (string required)
- modules POST: add .trim() check to reject whitespace-only id/nom
- users POST: add .trim() check to reject whitespace-only id/nom/prenom
- ues POST: add .trim() check to reject whitespace-only nom
- notes POST: add type check (typeof number) and bounds check (0 ≤ note ≤ 20)
- ue-modules POST: add coeff >= 0 validation

Update robustness tests to reflect fixed behavior (remove [BUG] labels,
replace assertRejects with status code assertions).

routes/(apps)/admin/api/modules/[idModule].ts

@@ -33,7 +33,16 @@ export const handler: Handlers<null, AuthenticatedState> = {
     request: Request,
     context: FreshContext<AuthenticatedState>,
   ): Promise<Response> {
-    const body: { nom: string } = await request.json();
+    let body: { nom: string };
+    try {
+      body = await request.json();
+    } catch {
+      return new Response(null, { status: 500 });
+    }
+
+    if (typeof body.nom !== "string") {
+      return new Response(null, { status: 400 });
+    }
 
     const [updated] = await db
       .update(modules)