feat(chat): 改为文本选择模式，全选仅作用于当前气泡

用 SelectionContainer 包住气泡/旁白/思维链/工具卡的正文，长按可拖选；移除长按整段复制的实现与其工具文件。

app/src/main/kotlin/top/yeij/cyrene/ui/chat/Clipboard.kt

@@ -1,32 +0,0 @@
-package top.yeij.cyrene.ui.chat
-
-import android.content.ClipData
-import android.content.ClipboardManager
-import android.content.Context
-import android.widget.Toast
-import androidx.compose.foundation.gestures.detectTapGestures
-import androidx.compose.runtime.Composable
-import androidx.compose.ui.Modifier
-import androidx.compose.ui.input.pointer.pointerInput
-import androidx.compose.ui.platform.LocalContext
-
-/**
- * 长按复制文本到系统剪贴板，并给一条 Toast 反馈。
- * 用框架的 ClipboardManager 而不是 Compose 的 LocalClipboardManager（后者在新版本已弃用）。
- */
-@Composable
-fun Modifier.copyOnLongPress(text: String): Modifier {
-    if (text.isBlank()) return this
-    val context = LocalContext.current
-    return this.pointerInput(text) {
-        detectTapGestures(
-            onLongPress = { copyToClipboard(context, text) },
-        )
-    }
-}
-
-private fun copyToClipboard(context: Context, text: String) {
-    val clipboard = context.getSystemService(Context.CLIPBOARD_SERVICE) as ClipboardManager
-    clipboard.setPrimaryClip(ClipData.newPlainText("Cyrene", text))
-    Toast.makeText(context, "已复制", Toast.LENGTH_SHORT).show()
-}

app/src/main/kotlin/top/yeij/cyrene/ui/chat/MessageBubble.kt

@@ -9,6 +9,7 @@ import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.widthIn
 import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.foundation.text.selection.SelectionContainer
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.remember
 import androidx.compose.ui.Alignment
@@ -34,6 +35,9 @@ private const val CURSOR = "▍"
  * - 其它 mode 原样整条渲染，不解析标签；
  * - `thinking` 非空时（来自 REST `/messages`，owner 可见）在气泡上方显示思维链卡片；
  * - `image` 非空时在气泡上方显示图片。
+ *
+ * 文本可自由选择：每个气泡/旁白各自包一层 [SelectionContainer]，
+ * 因此选择菜单的「全选」只作用于当前那一块，而不是整个页面。
  */
 @Composable
 fun MessageBubble(message: HistoryMessageDto) {
@@ -129,13 +133,14 @@ private fun Bubble(
 private fun AnnotationLine(parts: List<ContentPart>) {
     val text = parts.joinToString(" ") { it.text }.trim()
     if (text.isEmpty()) return
-    Text(
-        text = text,
-        style = MiuixTheme.textStyles.footnote1,
-        fontStyle = FontStyle.Italic,
-        color = MiuixTheme.colorScheme.onSurfaceVariantSummary,
-        modifier = Modifier.padding(horizontal = 8.dp, vertical = 2.dp),
-    )
+    SelectionContainer(modifier = Modifier.padding(horizontal = 8.dp, vertical = 2.dp)) {
+        Text(
+            text = text,
+            style = MiuixTheme.textStyles.footnote1,
+            fontStyle = FontStyle.Italic,
+            color = MiuixTheme.colorScheme.onSurfaceVariantSummary,
+        )
+    }
 }
 
 @Composable
@@ -143,7 +148,6 @@ private fun BubbleBody(text: String, isUser: Boolean) {
     Box(
         modifier = Modifier
             .widthIn(max = 300.dp)
-            .copyOnLongPress(text)
             .background(
                 color = if (isUser) {
                     MiuixTheme.colorScheme.primary
@@ -154,11 +158,13 @@ private fun BubbleBody(text: String, isUser: Boolean) {
             )
             .padding(horizontal = 14.dp, vertical = 10.dp),
     ) {
-        Text(
-            text = text,
-            style = MiuixTheme.textStyles.main,
-            color = if (isUser) MiuixTheme.colorScheme.onPrimary else MiuixTheme.colorScheme.onSurfaceContainer,
-        )
+        SelectionContainer {
+            Text(
+                text = text,
+                style = MiuixTheme.textStyles.main,
+                color = if (isUser) MiuixTheme.colorScheme.onPrimary else MiuixTheme.colorScheme.onSurfaceContainer,
+            )
+        }
     }
 }
 

app/src/main/kotlin/top/yeij/cyrene/ui/chat/StreamingBlocks.kt

@@ -11,6 +11,7 @@ import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.foundation.text.selection.SelectionContainer
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
@@ -24,8 +25,8 @@ import top.yukonga.miuix.kmp.basic.Text
 import top.yukonga.miuix.kmp.theme.MiuixTheme
 
 /**
- * 思维链卡片。默认展开（方便观察她的思考过程），可折叠。
- * 流式期间标题显示「思考中…」。
+ * 思维链卡片。流式期间展开（方便观察），流式结束自动折叠；历史思维链默认折叠。
+ * 正文包在 [SelectionContainer] 里，长按可自由选择、菜单「全选」只作用于本卡片。
  */
 @Composable
 fun ThinkingCard(
@@ -34,7 +35,6 @@ fun ThinkingCard(
     modifier: Modifier = Modifier,
 ) {
     if (text.isBlank() && !active) return
-    // 流式期间展开（方便观察），流式结束自动折叠；历史思维链默认折叠。
     var expanded by remember { mutableStateOf(active) }
     LaunchedEffect(active) {
         if (!active) expanded = false
@@ -126,9 +126,11 @@ private fun FoldCardLabel(text: String) {
 
 @Composable
 private fun FoldCardBody(text: String) {
-    Text(
-        text = text,
-        style = MiuixTheme.textStyles.footnote1,
-        color = MiuixTheme.colorScheme.onSurfaceVariantSummary,
-    )
+    SelectionContainer {
+        Text(
+            text = text,
+            style = MiuixTheme.textStyles.footnote1,
+            color = MiuixTheme.colorScheme.onSurfaceVariantSummary,
+        )
+    }
 }