Declarative subordinate devices + shared-machine check

CHANGELOG.md

@@ -88,6 +88,21 @@ ADR-007 and ADR-002.
   `computers_machinelink_alerts` setting that ships OFF: a site may legitimately
   run several PCs on one machine number, and there the alerts fire on correct
   data. The collector response warns either way.
+- A PC that drives a subordinate device is now declared, not coded. Two cases
+  had arrived separately and been written twice: a metrology PC drives a CMM or
+  Keyence unit that becomes a measuring-tool asset, and a part-marker PC drives
+  a marker that becomes a machine asset filed under its operation. Both mint a
+  device, link the PC with `controls` and archive that link on a re-image - one
+  mechanism with different nouns. They are now one map, and a site can add or
+  retarget an entry through a `subordinatedevice_<pctype>` setting, so the next
+  case - two marking lasers or two wax-trace units on one machine number - is
+  configuration rather than a code change. A malformed override falls back to
+  the default instead of failing the collector push.
+- `flask relationships check-shared-machines` reports machine numbers claimed
+  by more than one PC, and says which are modelled and which are faults. Several
+  devices genuinely sharing a number and two PCs mis-numbered at imaging look
+  identical from the outside; the difference is whether anything is filed under
+  the operation, which is what the check reports. Read-only.
 - A part marker is its own asset. Several Telesis markers can serve one
   operation number, so treating the operation as the marker collapsed separate
   devices into one record: their configurations, which differ by COM port,