feat: Linux 真实实现层 — 从存根库变为可用生产力工具

新增 _linux_impl.py (800+行):
- LinuxNetwork: 真实IP/接口/DNS/网关/MAC (ip命令+/proc/net)
- LinuxBluetooth: 真实蓝牙状态/扫描/配对/连接 (bluetoothctl)
- LinuxSensors: 真实温度/CPU频率/风扇 (/sys/class/hwmon)
- LinuxAudio: 真实音量控制/静音 (amixer)
- LinuxClipboard: 真实剪贴板读写 (xclip+tkinter回退)
- LinuxPower: 真实CPU/内存/电池 (psutil+/sys/class/power_supply)
- LinuxLocation: 真实IP地理定位 (ip-api.com)
- LinuxNotify: 真实桌面通知 (notify-send)
- LinuxDisplay: 真实屏幕尺寸/截屏/鼠标位置 (xdotool+X11)
- LinuxUIAutomation: 真实点击/输入/按键/滚动 (xdotool)
- LinuxCamera: 真实摄像头拍照 (opencv/V4L2)
- LinuxProcess: 真实进程列表/系统信息/应用管理 (psutil+/proc)
- LinuxShell: 真实命令执行 (subprocess)

改造10+核心类使用Linux真实实现:
- BluetoothAdapter/SensorManager/AudioManager
- ConnectivityManager/WifiManager/TelephonyManager
- LocationManager/PowerManager/BatteryManager/Build
- ActivityManager/Activity/Toast/Display/ClipboardManager
- NotificationManager

15项真实行为测试全部通过:
- 真实IP: 10.60.218.244
- 真实位置: 北京 39.9042, 116.407
- 真实主机名: work-41-vci-g427c
- 真实内核: 5.15.120.byteatom-ck.14
- 真实内存: 1.8GB/3.8GB
- 真实进程列表

android_pyapi/android/widget.py

@@ -14,6 +14,12 @@ from .view import (
     ViewGroup as VG,
 )
 
+try:
+    from .._linux_impl import IS_LINUX, LinuxNotify, LinuxClipboard
+    _USE_LINUX = IS_LINUX
+except ImportError:
+    _USE_LINUX = False
+
 
 # ═══════════════════════════════════════════════════════════════
 # TextView
@@ -3589,9 +3595,15 @@ class Toast(Stub):
         return toast
 
     def show(self):
-        pass
+        if _USE_LINUX:
+            LinuxNotify.send("Toast", self._text)
+        else:
+            print(f"[Toast] {self._text}")
 
     def cancel(self):
+        if _USE_LINUX:
+            # 桌面通知自动消失，无需操作
+            return
         pass
 
     def setGravity(self, gravity: int, x_offset: int, y_offset: int):