feat: completar fases 3 y 4 del roadmap mvp (gradebook, drag-and-drop, impersonacion) y actualizar README

frontend/src/app.js

@@ -189,10 +189,27 @@ app.use((req, res, next) => {
             };
         } catch (e) {}
     }
+    let isImpersonating = false;
+    let impersonatedUser = null;
+    if (user.is_admin() && req.cookies.impersonate_user_id) {
+        isImpersonating = true;
+        const targetId = req.cookies.impersonate_user_id;
+        try {
+            if (req.cookies.impersonate_user_data) {
+                impersonatedUser = JSON.parse(req.cookies.impersonate_user_data);
+            }
+        } catch (e) {}
+        if (!impersonatedUser) {
+            impersonatedUser = { id: targetId, name: `Usuario #${targetId}`, role: 'usuario' };
+        }
+    }
+
     req.user = user;
     res.locals.user = user;
     res.locals.current_user = user;
     res.locals.role = user.role;
+    res.locals.is_impersonating = isImpersonating;
+    res.locals.impersonated_user = impersonatedUser;
     res.locals.session = { get: (k, d) => d };
     res.locals.occupancy_metrics = { get: (k, d) => d };
     next();
@@ -259,6 +276,9 @@ app.use('/api', async (req, res) => {
         if (token) {
             headers['Authorization'] = `Bearer ${token}`;
         }
+        if (req.cookies.impersonate_user_id) {
+            headers['X-Impersonate-User'] = req.cookies.impersonate_user_id;
+        }
         const flaskUrl = `http://127.0.0.1:5000/api${req.url}`;
         const response = await axios({
             method: req.method,