feat(commands): add PC control packs — volume, apps, file_search, output_device

All four packs are pure Lua (sandbox=full) and call out to PowerShell helpers
where COM / native APIs are needed. No new Rust code, no rebuild required:
post_build.py --sync copies them under target/{debug,release}/resources/.

volume/
  - volume_up / volume_down: 5x VK_VOLUME_UP|DOWN via keybd_event
  - volume_mute: VK_VOLUME_MUTE
  - volume_max: 50x VK_VOLUME_UP (system clamps)
  Helper _volume_helper.ps1 P/Invokes user32!keybd_event.

apps/
  - open_browser  : start "" https://www.google.com (uses system default browser)
  - open_notepad  : notepad.exe
  - open_calculator: calc.exe
  - open_explorer : explorer.exe
  - open_terminal : wt.exe, falls back to powershell.exe
  - open_settings : ms-settings: protocol
  - open_task_manager: taskmgr.exe
  - lock_screen   : rundll32 user32.dll,LockWorkStation
  - screenshot    : System.Drawing capture to ~/Pictures/jarvis_screenshot_*.png

file_search/
  - find file <query> : recursive Get-ChildItem in Desktop/Documents/Downloads
    (depth 3, top 5 matches). Strips Russian/English/Ukrainian trigger
    prefixes from the recognized phrase, then opens explorer /select on the
    first hit and notifies with the total count.

output_device/
  - list_output_devices : enumerates active render endpoints via
    IMMDeviceEnumerator and notifies friendly names with indices
  - next_output_device  : cycles the system default render device via the
    undocumented IPolicyConfig::SetDefaultEndpoint (eConsole/Multimedia/
    Communications). Tested locally — listed 7 devices, current correctly
    identified at index 5.

resources/commands/volume/_volume_helper.ps1

@@ -0,0 +1,31 @@
+param(
+    [Parameter(Mandatory=$true)]
+    [ValidateSet("up","down","mute","max")]
+    [string]$Action,
+
+    [int]$Times = 1
+)
+
+Add-Type -Name VolumeKey -Namespace Win32 -MemberDefinition @'
+[DllImport("user32.dll")]
+public static extern void keybd_event(byte bVk, byte bScan, uint dwFlags, System.UIntPtr dwExtraInfo);
+'@
+
+$KEY_UP   = 0xAF
+$KEY_DOWN = 0xAE
+$KEY_MUTE = 0xAD
+
+$vk = switch ($Action) {
+    "up"   { $KEY_UP }
+    "down" { $KEY_DOWN }
+    "mute" { $KEY_MUTE }
+    "max"  { $KEY_UP }
+}
+
+$count = if ($Action -eq "max") { 50 } else { $Times }
+
+for ($i = 0; $i -lt $count; $i++) {
+    [Win32.VolumeKey]::keybd_event($vk, 0, 0, [UIntPtr]::Zero)
+    [Win32.VolumeKey]::keybd_event($vk, 0, 2, [UIntPtr]::Zero)
+    Start-Sleep -Milliseconds 25
+}