feat: command snippets + UI test coverage for new features

- core/snippets.py: SnippetManager with 20 prebuilt sysadmin commands,
  CRUD + reorder, persisted to ~/.sshclient/snippets.json
- ui/snippet_dialog.py: SnippetDialog (add/edit) + SnippetManagerDialog
  (table view with add/edit/delete/move up/down)
- ui/terminal_panel.py: snippet combo box in toolbar, send_command()
  method to inject commands into interactive shell, snippet manager button
- README.md: updated feature table, usage section, project structure
- test_ui.py: added [2/4] checks for sparkline/snippets/theme,
  added [4/4] theme toggle verification

ui/snippet_dialog.py

@@ -0,0 +1,151 @@
+"""
+命令片段管理对话框
+"""
+from PyQt5.QtCore import Qt
+from PyQt5.QtWidgets import (
+    QDialog, QVBoxLayout, QHBoxLayout, QTableWidget, QTableWidgetItem,
+    QPushButton, QLabel, QLineEdit, QTextEdit, QMessageBox, QHeaderView,
+    QAbstractItemView, QSplitter, QWidget, QFormLayout,
+)
+
+from core.snippets import SnippetManager
+
+
+class SnippetDialog(QDialog):
+    """单个片段的编辑/新增对话框"""
+
+    def __init__(self, parent=None, name: str = "", cmd: str = ""):
+        super().__init__(parent)
+        self.setWindowTitle("编辑片段" if name else "新增片段")
+        self.setMinimumWidth(460)
+        v = QVBoxLayout(self)
+        form = QFormLayout()
+        self.name_edit = QLineEdit(name)
+        self.name_edit.setPlaceholderText("如：查看端口占用")
+        form.addRow("名称:", self.name_edit)
+        self.cmd_edit = QTextEdit(cmd)
+        self.cmd_edit.setPlaceholderText("如：ss -tlnp | grep :80")
+        self.cmd_edit.setMaximumHeight(80)
+        form.addRow("命令:", self.cmd_edit)
+        v.addLayout(form)
+        btns = QHBoxLayout()
+        btns.addStretch(1)
+        ok = QPushButton("保存")
+        ok.clicked.connect(self._on_ok)
+        cancel = QPushButton("取消")
+        cancel.clicked.connect(self.reject)
+        btns.addWidget(ok)
+        btns.addWidget(cancel)
+        v.addLayout(btns)
+
+    def _on_ok(self):
+        if not self.name_edit.text().strip():
+            QMessageBox.warning(self, "提示", "请输入名称")
+            return
+        if not self.cmd_edit.toPlainText().strip():
+            QMessageBox.warning(self, "提示", "请输入命令")
+            return
+        self.accept()
+
+    def get_value(self) -> dict:
+        return {
+            "name": self.name_edit.text().strip(),
+            "cmd": self.cmd_edit.toPlainText().strip(),
+        }
+
+
+class SnippetManagerDialog(QDialog):
+    """片段管理主对话框：表格 + 增删改 + 上下移"""
+
+    def __init__(self, mgr: SnippetManager, parent=None):
+        super().__init__(parent)
+        self.mgr = mgr
+        self.setWindowTitle("命令片段管理")
+        self.setMinimumSize(520, 420)
+        self._build_ui()
+        self._refresh_table()
+
+    def _build_ui(self):
+        v = QVBoxLayout(self)
+        # 工具栏
+        toolbar = QHBoxLayout()
+        toolbar.addWidget(QLabel("📋 命令片段列表"))
+        toolbar.addStretch(1)
+        self.btn_add = QPushButton("➕ 新增")
+        self.btn_add.clicked.connect(self._add)
+        self.btn_edit = QPushButton("✏ 编辑")
+        self.btn_edit.clicked.connect(self._edit)
+        self.btn_del = QPushButton("🗑 删除")
+        self.btn_del.clicked.connect(self._delete)
+        self.btn_up = QPushButton("⬆ 上移")
+        self.btn_up.clicked.connect(lambda: self._move(-1))
+        self.btn_down = QPushButton("⬇ 下移")
+        self.btn_down.clicked.connect(lambda: self._move(1))
+        for b in (self.btn_add, self.btn_edit, self.btn_del, self.btn_up, self.btn_down):
+            toolbar.addWidget(b)
+        v.addLayout(toolbar)
+        # 表格
+        self.table = QTableWidget(0, 2)
+        self.table.setHorizontalHeaderLabels(["名称", "命令"])
+        self.table.horizontalHeader().setSectionResizeMode(0, QHeaderView.ResizeToContents)
+        self.table.horizontalHeader().setSectionResizeMode(1, QHeaderView.Stretch)
+        self.table.setSelectionBehavior(QAbstractItemView.SelectRows)
+        self.table.setEditTriggers(QAbstractItemView.NoEditTriggers)
+        self.table.doubleClicked.connect(self._edit)
+        v.addWidget(self.table)
+        # 关闭按钮
+        btns = QHBoxLayout()
+        btns.addStretch(1)
+        close = QPushButton("关闭")
+        close.clicked.connect(self.accept)
+        btns.addWidget(close)
+        v.addLayout(btns)
+
+    def _refresh_table(self):
+        snippets = self.mgr.list_all()
+        self.table.setRowCount(len(snippets))
+        for i, s in enumerate(snippets):
+            self.table.setItem(i, 0, QTableWidgetItem(s["name"]))
+            cmd_display = s["cmd"][:60] + ("..." if len(s["cmd"]) > 60 else "")
+            self.table.setItem(i, 1, QTableWidgetItem(cmd_display))
+            self.table.item(i, 0).setToolTip(s["cmd"])
+
+    def _add(self):
+        dlg = SnippetDialog(self)
+        if dlg.exec_() == dlg.Accepted:
+            v = dlg.get_value()
+            self.mgr.add(v["name"], v["cmd"])
+            self._refresh_table()
+
+    def _edit(self):
+        row = self.table.currentRow()
+        if row < 0:
+            return
+        s = self.mgr.list_all()[row]
+        dlg = SnippetDialog(self, s["name"], s["cmd"])
+        if dlg.exec_() == dlg.Accepted:
+            v = dlg.get_value()
+            self.mgr.update(row, v["name"], v["cmd"])
+            self._refresh_table()
+
+    def _delete(self):
+        row = self.table.currentRow()
+        if row < 0:
+            return
+        s = self.mgr.list_all()[row]
+        if QMessageBox.question(
+            self, "确认删除", f"删除片段「{s['name']}」？",
+            QMessageBox.Yes | QMessageBox.No
+        ) == QMessageBox.Yes:
+            self.mgr.remove(row)
+            self._refresh_table()
+
+    def _move(self, direction):
+        row = self.table.currentRow()
+        if row < 0:
+            return
+        self.mgr.move(row, direction)
+        new_row = row + direction
+        self._refresh_table()
+        if 0 <= new_row < self.table.rowCount():
+            self.table.selectRow(new_row)