feat(chat): implement ChatArea Compose UI component

app/src/main/java/com/stand/standapp/ui/chat/components/ChatArea.kt

@@ -0,0 +1,101 @@
+package com.stand.standapp.ui.chat.components
+
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.*
+import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.lazy.items
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.Menu
+import androidx.compose.material.icons.filled.Send
+import androidx.compose.material3.*
+import androidx.compose.runtime.*
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.unit.dp
+import com.stand.standapp.ui.chat.model.ChatMessage
+
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+fun ChatArea(
+    messages: List<ChatMessage>,
+    onSendMessage: (String) -> Unit,
+    onOpenDrawer: () -> Unit,
+    onClose: () -> Unit
+) {
+    var inputText by remember { mutableStateOf("") }
+
+    Column(modifier = Modifier.fillMaxSize().background(Color.White)) {
+        // 顶部栏
+        TopAppBar(
+            title = { Text("AI 助手", style = MaterialTheme.typography.titleMedium) },
+            navigationIcon = {
+                IconButton(onClick = onOpenDrawer) {
+                    Icon(Icons.Default.Menu, contentDescription = "Menu")
+                }
+            },
+            actions = {
+                TextButton(onClick = onClose) { Text("关闭") }
+            },
+            colors = TopAppBarDefaults.topAppBarColors(containerColor = Color(0xFFF3F4F6))
+        )
+
+        // 消息列表
+        LazyColumn(
+            modifier = Modifier.weight(1f).fillMaxWidth().padding(horizontal = 12.dp),
+            contentPadding = PaddingValues(vertical = 12.dp),
+            verticalArrangement = Arrangement.spacedBy(8.dp)
+        ) {
+            items(messages) { msg ->
+                val isUser = msg.role == ChatMessage.Role.USER
+                Box(
+                    modifier = Modifier.fillMaxWidth(),
+                    contentAlignment = if (isUser) Alignment.CenterEnd else Alignment.CenterStart
+                ) {
+                    Surface(
+                        shape = RoundedCornerShape(12.dp),
+                        color = if (isUser) Color(0xFF10B981) else Color(0xFFE5E7EB),
+                        contentColor = if (isUser) Color.White else Color.Black
+                    ) {
+                        Text(
+                            text = msg.content + if (msg.isStreaming) " █" else "",
+                            modifier = Modifier.padding(12.dp),
+                            style = MaterialTheme.typography.bodyMedium
+                        )
+                    }
+                }
+            }
+        }
+
+        // 输入区
+        Row(
+            modifier = Modifier
+                .fillMaxWidth()
+                .padding(8.dp)
+                .navigationBarsPadding() // 处理底部内边距
+                .imePadding(), // 键盘避让
+            verticalAlignment = Alignment.CenterVertically
+        ) {
+            OutlinedTextField(
+                value = inputText,
+                onValueChange = { inputText = it },
+                modifier = Modifier.weight(1f),
+                placeholder = { Text("输入你想问的问题...") },
+                shape = RoundedCornerShape(20.dp)
+            )
+            Spacer(modifier = Modifier.width(8.dp))
+            IconButton(
+                onClick = {
+                    if (inputText.isNotBlank()) {
+                        onSendMessage(inputText)
+                        inputText = ""
+                    }
+                },
+                modifier = Modifier.background(Color(0xFF10B981), RoundedCornerShape(50))
+            ) {
+                Icon(Icons.Default.Send, contentDescription = "Send", tint = Color.White)
+            }
+        }
+    }
+}