feat: show last search query in session history

- Added last_query field to SearchSession interface
- loadSessions now fetches last user message for each session
- Session list displays: mode badge, title, last query, message count, time
- Added .hs-query CSS style for query text

src/views/SearchView.vue

@@ -44,7 +44,8 @@
                   <span class="hs-mode">{{ formatMode(s.mode) }}</span>
                   <div class="hs-title" @click="handleSelectSession(s)">{{ s.title }}</div>
                 </div>
-                <div class="hs-time">{{ s.message_count }} messages · {{ formatSessionTime(s.updated_at) }}</div>
+                <div v-if="s.last_query" class="hs-query">{{ s.last_query.slice(0, 30) }}{{ s.last_query.length > 30 ? '...' : '' }}</div>
+                <div class="hs-time">{{ s.message_count }} msgs · {{ formatSessionTime(s.updated_at) }}</div>
               </div>
               <button class="hs-menu-btn" @click.stop="toggleSessionMenu(s.id)">⋯</button>
               <div v-if="activeSessionMenu === s.id" class="hs-menu">
@@ -1892,6 +1893,13 @@ function openSource(src: SourceInfo) {
   overflow: hidden;
   text-overflow: ellipsis;
 }
+.hs-query {
+  font-size: 11px;
+  color: var(--text-secondary);
+  white-space: nowrap;
+  overflow: hidden;
+  text-overflow: ellipsis;
+}
 .hs-item.pinned .hs-time { color: rgba(var(--primary-color-rgb), 0.8); }
 .hs-mode {
   font-size: 10px;