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/collectors/linux.py

@@ -80,7 +80,7 @@ def collect_local_linux(stage=lambda message: None, cancelled=lambda: False, run
     started = time.monotonic()
     data = {'schema_version': '1.0', 'synthetic': False,
             'collected_at': datetime.now(timezone.utc).isoformat(),
-            'server': {'hostname': socket.gethostname() if privacy_policy['approved_hostnames'] else 'Host-0001', 'platform': 'linux',
+            'server': {'hostname': socket.gethostname() if privacy_policy['approved_hostnames'] or privacy_policy['retain']['hostname'] else 'Host-0001', 'platform': 'linux',
                        'collection_source': 'Local Linux read-only collection',
                        'operating_system': platform.system(), 'os_build': platform.release(),
                        'last_boot': 'Not collected', 'ip_addresses': [], 'network_adapters': [],