ghidra-mcp-setup.ps1 installs in the wrong directory

Hello, just a minor issue.

I have both Ghidra 12.0 and 12.0.2 installed.

In this case, ghidra-mcp-setup.ps1 installs the JAR file in `$env:USERPROFILE\AppData\Roaming\ghidra\ghidra_12.0_PUBLIC\` instead of `$env:USERPROFILE\AppData\Roaming\ghidra\ghidra_12.0.2_PUBLIC\`.

This is due to the following lines (880-888):
```
    if (Test-Path $ghidraUserBase) {
        # Find the most recent ghidra version directory
        $ghidraVersionDirs = Get-ChildItem -Path $ghidraUserBase -Directory -Filter "ghidra_*" |
                             Sort-Object Name -Descending
        if ($ghidraVersionDirs) {
            $ghidraVersionDir = $ghidraVersionDirs[0].Name
            Write-LogInfo "Detected Ghidra user config version: $ghidraVersionDir"
        }
    }
```
And `ghidra_12.0_PUBLIC` comes before `ghidra_12.0.2_PUBLIC`.

IMHO I would just keep the logic marked as fallback (lines 890-898). You already know the Ghidra version, so just choose the corresponding user config folder, there's no need to detect what other folders are present. I would rather make the script fail if the corresponding  user config folder is not found, which may happen if you've just installed a new Ghidra version and you haven't run it yet.

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