Retain infrastructure names and share/mount roots behind policy switches

Add a `retain` block to privacy_policy.json (all on by default) so assessments
show software, services, processes, tasks, shares/mounts and private peer IPs.
Values pass an identifier-pattern filter (digit runs, SSN/phone, e-mail, charset,
length, path depth). Accounts, command lines, child paths, filenames and public
peer IPs stay omitted. Linux collector and Windows PowerShell collectors updated;
tests cover retention, withholding and all-switches-off.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

powershell/Get-ServerSystem.ps1

@@ -8,7 +8,7 @@ function Get-SamsaraSystem {
         domain = 'Not collected'; domain_joined = $null
     }
     Get-SamsaraPrivacyConfiguration
-    if ($script:SamsaraPrivacy.approved_hostnames -ccontains [Environment]::MachineName) { $Result.data.hostname = [Environment]::MachineName }
+    if (($script:SamsaraPrivacy.approved_hostnames -ccontains [Environment]::MachineName) -or (Test-SamsaraRetain 'hostname' ([Environment]::MachineName))) { $Result.data.hostname = [Environment]::MachineName }
     Invoke-SamsaraRead $Result 'OS identity' {
         $os = Get-CimInstance -ClassName Win32_OperatingSystem -Property Version,BuildNumber,LastBootUpTime,ProductType -ErrorAction Stop
         $years = @{ '14393' = '2016'; '17763' = '2019'; '20348' = '2022'; '26100' = '2025' }