feat: add quick action buttons (preview/undo/reset) to sidebar

Sidebar now has 快捷操作 section matching Streamlit app functionality:
- 预览 — sends "预览报表" to preview current JRXML
- 撤销 — sends "撤销上一步修改" to revert last change
- 重置 — sends "重新来，清空当前报表" to reset session

Session store now tracks history_states for undo availability check.

frontend/src/App.vue

@@ -114,7 +114,7 @@ async function handleSend(text: string, files: File[]) {
 
 <template>
   <div class="app-layout">
-    <Sidebar />
+    <Sidebar @quickAction="(text) => handleSend(text, [])" />
 
     <main class="main-area">
       <div class="chat-container" ref="chatContainer">

frontend/src/components/Sidebar.vue

@@ -6,6 +6,22 @@ import { useChatStore } from '../stores/chat'
 const session = useSessionStore()
 const chat = useChatStore()
 
+const emit = defineEmits<{
+  quickAction: [text: string]
+}>()
+
+function handlePreview() {
+  emit('quickAction', '预览报表')
+}
+
+function handleUndo() {
+  emit('quickAction', '撤销上一步修改')
+}
+
+function handleReset() {
+  emit('quickAction', '重新来，清空当前报表')
+}
+
 onMounted(() => {
   session.loadSessions()
 })
@@ -63,6 +79,26 @@ async function handleDelete() {
       </button>
     </div>
 
+    <div class="sidebar-section" v-if="session.currentId">
+      <div class="section-title">快捷操作</div>
+      <div class="quick-actions">
+        <button
+          class="btn-action btn-preview"
+          :disabled="!session.hasJrxml"
+          @click="handlePreview"
+        >预览</button>
+        <button
+          class="btn-action btn-undo"
+          :disabled="!session.hasHistory"
+          @click="handleUndo"
+        >撤销</button>
+        <button
+          class="btn-action btn-reset"
+          @click="handleReset"
+        >重置</button>
+      </div>
+    </div>
+
     <div class="sidebar-section" v-if="session.currentJrxml || session.versions.length > 0">
       <div class="section-title">下载</div>
       <a
@@ -207,6 +243,60 @@ async function handleDelete() {
   color: #1e1e2e;
 }
 
+.quick-actions {
+  display: flex;
+  gap: 6px;
+  padding: 0 16px;
+}
+
+.btn-action {
+  flex: 1;
+  padding: 6px 8px;
+  border: 1px solid #45475a;
+  background: #313244;
+  color: #cdd6f4;
+  border-radius: 6px;
+  cursor: pointer;
+  font-size: 12px;
+  transition: background 0.15s, border-color 0.15s;
+}
+
+.btn-action:hover:not(:disabled) {
+  background: #45475a;
+}
+
+.btn-action:disabled {
+  opacity: 0.4;
+  cursor: not-allowed;
+}
+
+.btn-preview {
+  border-color: #89b4fa;
+}
+
+.btn-preview:hover:not(:disabled) {
+  background: #89b4fa;
+  color: #1e1e2e;
+}
+
+.btn-undo {
+  border-color: #f9e2af;
+}
+
+.btn-undo:hover:not(:disabled) {
+  background: #f9e2af;
+  color: #1e1e2e;
+}
+
+.btn-reset {
+  border-color: #f38ba8;
+}
+
+.btn-reset:hover:not(:disabled) {
+  background: #f38ba8;
+  color: #1e1e2e;
+}
+
 .btn-download {
   display: block;
   padding: 8px 16px;

frontend/src/stores/session.ts

@@ -9,8 +9,12 @@ export const useSessionStore = defineStore('session', () => {
   const currentId = ref<string>('')
   const currentName = ref<string>('')
   const versions = ref<any[]>([])
+  const historyStates = ref<any[]>([])
   const currentJrxml = ref<string>('')
 
+  const hasJrxml = computed(() => !!currentJrxml.value)
+  const hasHistory = computed(() => historyStates.value.length > 0)
+
   const sortedSessions = computed(() =>
     [...sessions.value].sort((a, b) =>
       new Date(b.updated_at).getTime() - new Date(a.updated_at).getTime()
@@ -43,6 +47,7 @@ export const useSessionStore = defineStore('session', () => {
       const state = data.agent_state
       currentJrxml.value = state.current_jrxml || ''
       versions.value = state.jrxml_versions || []
+      historyStates.value = state.history_states || []
     } catch (e) {
       console.error('加载会话失败:', e)
     }
@@ -61,11 +66,12 @@ export const useSessionStore = defineStore('session', () => {
   function refreshFromState(agentState: Record<string, any>) {
     currentJrxml.value = agentState.current_jrxml || currentJrxml.value
     versions.value = agentState.jrxml_versions || versions.value
+    historyStates.value = agentState.history_states || historyStates.value
   }
 
   return {
-    sessions, currentId, currentName, versions, currentJrxml,
+    sessions, currentId, currentName, versions, historyStates, currentJrxml,
-    sortedSessions, currentSession,
+    hasJrxml, hasHistory, sortedSessions, currentSession,
     loadSessions, createSession, switchSession, deleteCurrent, refreshFromState,
   }
 })