fix: properly cleanup Windows process tree on Obsidian exit

[Gerkinfeltser]

Problem

On Windows, when Obsidian is closed with the OpenCode panel open, the server process (node.exe) is not terminated and becomes an orphaned process. This happens because:

1. The server is spawned with shell: true, which creates cmd.exe → node.exe
2. The PID captured is cmd.exe, not the actual node.exe
3. When Obsidian exits, onunload() tries to kill the PID, but cmd.exe dies leaving node.exe orphaned
4. The child process lookup using WMIC was failing silently

Solution

Store the PID separately in main.ts and use PowerShell to reliably find and kill child processes:

1. Store PID separately: Added serverPid field to track the process PID independently of ProcessManager (which gets destroyed before onunload() fires)
2. PowerShell child lookup: Replaced WMIC with PowerShell's Get-CimInstance which is more reliable on modern Windows
3. beforeunload handler: Added cleanup handler for window close event (more reliable than onunload on Windows)
4. Triple-kill strategy:
   • Kill child processes (actual node.exe) using PowerShell
   • Kill parent process (cmd.exe)
   • Fallback: kill by command line pattern using WMIC (port-based)

Testing

Tested on Windows 11:

• Server starts correctly
• Server stops when clicking panel close button
• Server stops when closing Obsidian window
• No orphaned node.exe processes after exit

Breaking Changes

None. The fix maintains backward compatibility.