feat(exam-prep F8): слабые темы на дашборде + strategy=weak в тренажёре

frontend/css/exam-prep.css

@@ -800,6 +800,49 @@
   width: 12px; height: 12px; aspect-ratio: 1;
 }
 
+/* Weak topics widget */
+.dh-weak-rows { display: flex; flex-direction: column; gap: 8px; }
+.dh-weak-row {
+  display: grid;
+  grid-template-columns: 1fr auto auto;
+  align-items: center;
+  gap: 12px;
+  padding: 11px 14px;
+  border: 1.5px solid var(--border);
+  border-radius: 10px;
+  text-decoration: none;
+  color: var(--text);
+  background: var(--surface);
+  transition: all .15s;
+}
+.dh-weak-row:hover {
+  border-color: #E63946;
+  background: rgba(230,57,70,.04);
+}
+.dh-weak-info { min-width: 0; }
+.dh-weak-title {
+  font-family: 'Unbounded', sans-serif; font-size: .9rem; font-weight: 700;
+}
+.dh-weak-meta {
+  font-size: .75rem; color: var(--text-3); margin-top: 2px;
+}
+.dh-weak-accuracy {
+  font-family: 'Unbounded', sans-serif; font-size: 1rem; font-weight: 800;
+  color: #E63946;
+  padding: 4px 10px; border-radius: 7px;
+  background: rgba(230,57,70,.10);
+}
+.dh-weak-cta {
+  display: inline-flex; align-items: center; gap: 4px;
+  font-size: .78rem; font-weight: 700; color: var(--violet);
+  white-space: nowrap;
+}
+.dh-weak-cta svg { width: 13px; height: 13px; }
+@media (max-width: 540px) {
+  .dh-weak-row { grid-template-columns: 1fr auto; }
+  .dh-weak-cta { display: none; }
+}
+
 /* Recent mocks rows */
 .dh-mock-row {
   display: grid;