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)/notes/api/ues.ts

@@ -24,7 +24,7 @@ export const handler: Handlers = {
       const body = await request.json();
       const { nom } = body;
 
-      if (!nom) {
+      if (!nom || !nom.trim()) {
         return new Response("Champ 'nom' manquant", { status: 400 });
       }