Printer assignment end to end, and a container that keeps a site's files

Assign printers to a MACHINE and let whichever PC controls it install them, with
the observed half kept strictly apart from the assigned half: a collector report
can never write an assignment row. Adoption is explicit. Adds a singular
relationship type so defaultprinter can mean exactly one, client scripts that
converge a bay's queues and correct a drifted one in place, and a wave gate so a
fleet-wide driver rollout cannot stampede its own share.

On the container side: the compose stack never persisted the instance directory,
so a rebuild discarded plugins.json and every upload. It is a volume now, the
image ships instance/ owned by the app user so the mountpoint is writable, and
the database moves to MySQL 8.4 LTS, which the Windows runbook has recommended
since 8.0 went end of life. The image also could not build at all: the frontend
stage never copied the plugin staging script it runs.

Adds a topology migration guide covering IIS to Docker and back.

plugins/computers/plugin.py

@@ -162,6 +162,25 @@ class ComputersPlugin(BasePlugin):
             },
         }
 
+    def get_settings_cards(self) -> List[dict]:
+        """The asset reporter's own settings page.
+
+        It is a settings card rather than a docs page because it does two things
+        an operator needs at the same moment: name this site's routable ranges,
+        and download the reporter that carries them.
+        """
+        return [
+            {
+                'group': 'Computers',
+                'to': '/settings/collector',
+                'icon': 'download',
+                'title': 'Asset reporter',
+                'description': 'Download the collector script stamped with this '
+                               'site\'s URL and ranges',
+                'position': 26,
+            },
+        ]
+
     def get_settings_defaults(self) -> List[dict]:
         """Settings this plugin owns.
 
@@ -178,6 +197,19 @@ class ComputersPlugin(BasePlugin):
                 'description': 'Hours without a collector report before a PC '
                                'is listed as not reporting on the dashboard.',
             },
+            {
+                'key': 'computers_routableranges',
+                'value': '',
+                'valuetype': 'string',
+                'category': 'computers',
+                'description': 'Comma-separated CIDRs naming this site\'s '
+                               'routable ranges, e.g. 10.20.0.0/23,10.21.4.0/26. '
+                               'Stamped into the collector script this server '
+                               'generates, so a bay with a controller NIC and a '
+                               'corporate NIC reports the right one. Blank uses '
+                               'the NIC carrying the default route, which needs '
+                               'no knowledge of a site\'s addressing.',
+            },
             {
                 'key': 'computers_machinelink_alerts',
                 'value': 'false',