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/ue-modules.ts

@@ -47,6 +47,12 @@ export const handler: Handlers = {
         );
       }
 
+      if (typeof coeff !== "number" || coeff < 0) {
+        return new Response("Champ 'coeff' doit être un nombre >= 0", {
+          status: 400,
+        });
+      }
+
       const result = await db.insert(ueModules).values({
         idModule,
         idUE,