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/terminal_panel.py

@@ -21,6 +21,7 @@ from PyQt5.QtWidgets import (
 )
 
 from core.ssh_client import SSHConnection
+from core.snippets import SnippetManager
 
 
 # ANSI 颜色映射（16 色）
@@ -133,6 +134,8 @@ class TerminalPanel(QWidget):
         self._ansi_invert = False
         # OSC 0/2 设置的窗口标题
         self._window_title = ""
+        # 命令片段
+        self.snippet_mgr = SnippetManager()
 
         self._build_ui()
         self._apply_style()
@@ -152,6 +155,20 @@ class TerminalPanel(QWidget):
         self.status_label.setStyleSheet("color: #888;")
         toolbar.addWidget(self.status_label)
         toolbar.addStretch(1)
+        # 命令片段
+        toolbar.addWidget(QLabel("📋"))
+        self.snippet_combo = QComboBox()
+        self.snippet_combo.setMinimumWidth(180)
+        self.snippet_combo.setToolTip("选择命令片段快速发送到终端")
+        self.snippet_combo.currentIndexChanged.connect(self._on_snippet_selected)
+        toolbar.addWidget(self.snippet_combo)
+        self._refresh_snippets()
+        self.btn_snippet_mgr = QPushButton("⚙")
+        self.btn_snippet_mgr.setFixedWidth(28)
+        self.btn_snippet_mgr.setToolTip("管理命令片段")
+        self.btn_snippet_mgr.clicked.connect(self._open_snippet_manager)
+        toolbar.addWidget(self.btn_snippet_mgr)
+        toolbar.addSpacing(8)
         self.btn_clear = QPushButton("清屏")
         self.btn_clear.clicked.connect(self._clear_screen)
         self.btn_reset = QPushButton("重连 shell")
@@ -190,6 +207,51 @@ class TerminalPanel(QWidget):
             }
         """)
 
+    # ============================================================
+    # 命令片段
+    # ============================================================
+    def _refresh_snippets(self):
+        """刷新下拉框"""
+        self.snippet_combo.blockSignals(True)
+        self.snippet_combo.clear()
+        self.snippet_combo.addItem("-- 选择命令片段 --", "")
+        for s in self.snippet_mgr.list_all():
+            self.snippet_combo.addItem(f"{s['name']}  ({s['cmd'][:30]})", s["cmd"])
+        self.snippet_combo.blockSignals(False)
+
+    def _on_snippet_selected(self, index: int):
+        """选择片段后发送命令到终端"""
+        if index <= 0:
+            return
+        cmd = self.snippet_combo.itemData(index)
+        if not cmd:
+            return
+        # 重置下拉框选中项（让用户能重复选同一个）
+        self.snippet_combo.blockSignals(True)
+        self.snippet_combo.setCurrentIndex(0)
+        self.snippet_combo.blockSignals(False)
+        # 发送命令
+        self.send_command(cmd)
+
+    def send_command(self, cmd: str):
+        """发送一条命令到远程 shell（自动加换行）"""
+        if not self.chan or not self._connected:
+            self._set_status("未连接，无法发送命令", "#c62828")
+            return
+        data = cmd.encode("utf-8", errors="replace")
+        if not cmd.endswith("\n"):
+            data += b"\n"
+        try:
+            self.chan.send(data)
+        except Exception as e:
+            self._set_status(f"发送失败: {e}", "#c62828")
+
+    def _open_snippet_manager(self):
+        from .snippet_dialog import SnippetManagerDialog
+        dlg = SnippetManagerDialog(self.snippet_mgr, self)
+        dlg.exec_()
+        self._refresh_snippets()
+
     # ============================================================
     # 生命周期
     # ============================================================