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>

samsara/assets/privacy_policy.json

@@ -5,5 +5,14 @@
   "approved_share_roots": [],
   "approved_service_names": [],
   "approved_software_names": [],
-  "max_session_assessments": 10
+  "max_session_assessments": 10,
+  "retain": {
+    "hostname": true,
+    "software_names": true,
+    "service_names": true,
+    "process_names": true,
+    "task_names": true,
+    "storage_names_and_roots": true,
+    "private_peer_addresses": true
+  }
 }