Make gauge/maintenance identifiers per-asset-type and extend to all types

Optional asset identifiers (gauge lab reference, maintenance reference, FQDN)
were global per-identifier and only surfaced on equipment. Now they are
toggleable per asset type and rendered on every asset type.

- settings: replace 3 global identifier toggles with a per-type matrix. New
  keys identifier_<name>_<assettype>_enabled (3 identifiers x 4 types).
  IDENTIFIER_LABELS / IDENTIFIER_ASSETTYPES constants drive the seed (API seed
  and CLI seed settings).
- composable: identifierSettings now exposes isEnabled(name, assettype),
  per-type flag winning over the legacy global key, defaulting on.
- backend writes: computers, network, printers asset create + update now
  accept gaugelabreference and maintenancereference (equipment already did).
  Reads already flowed through Asset.to_dict.
- frontend: Settings page renders an identifier x asset-type toggle matrix.
  Equipment, PC, printer, network forms and detail pages show gauge/maintenance
  (and FQDN where applicable) gated by isEnabled(name, type).

Legacy global identifier_<name>_enabled keys are still honored as a fallback
for older installs. SystemSettings toggles upsert (create on 404) so a deploy
that has not re-seeded still works on first toggle.

144 tests pass, naming/style check green, frontend builds. Verified live:
matrix renders, PC form shows the fields, PUT persists gauge/maintenance on a
PC and reads back.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/views/printers/PrinterForm.vue

@@ -37,7 +37,7 @@
         </div>
 
         <div class="form-row">
-          <div class="form-group" v-if="identifierflags.fqdn">
+          <div class="form-group" v-if="isEnabled('fqdn', 'printer')">
             <label for="hostname">Hostname (FQDN)</label>
             <input
               id="hostname"
@@ -61,6 +61,28 @@
           </div>
         </div>
 
+        <div class="form-row" v-if="isEnabled('gaugelabreference', 'printer') || isEnabled('maintenancereference', 'printer')">
+          <div class="form-group" v-if="isEnabled('gaugelabreference', 'printer')">
+            <label for="gaugelabreference">Gauge Lab Reference</label>
+            <input
+              id="gaugelabreference"
+              v-model="form.gaugelabreference"
+              type="text"
+              class="form-control"
+            />
+          </div>
+
+          <div class="form-group" v-if="isEnabled('maintenancereference', 'printer')">
+            <label for="maintenancereference">Maintenance Reference</label>
+            <input
+              id="maintenancereference"
+              v-model="form.maintenancereference"
+              type="text"
+              class="form-control"
+            />
+          </div>
+        </div>
+
         <div class="form-row">
           <div class="form-group">
             <label for="machinetypeid">Printer Type *</label>
@@ -273,7 +295,7 @@ import Modal from '../../components/Modal.vue'
 import { currentTheme } from '../../stores/theme'
 import { useIdentifierFlags } from '../../composables/identifierSettings'
 
-const identifierflags = useIdentifierFlags()
+const { isEnabled } = useIdentifierFlags()
 
 const route = useRoute()
 const router = useRouter()
@@ -293,6 +315,8 @@ const form = ref({
   alias: '',
   hostname: '',
   serialnumber: '',
+  gaugelabreference: '',
+  maintenancereference: '',
   machinetypeid: '',
   statusid: '',
   vendorid: '',
@@ -462,6 +486,8 @@ onMounted(async () => {
         alias: printer.name && printer.name.toUpperCase() !== 'NONE' ? printer.name : '',
         hostname: ext.hostname || '',
         serialnumber: printer.serialnumber || '',
+        gaugelabreference: printer.gaugelabreference || '',
+        maintenancereference: printer.maintenancereference || '',
         machinetypeid: ext.printertypeid || '',
         statusid: printer.statusid || '',
         vendorid: ext.vendorid || '',
@@ -520,6 +546,8 @@ async function savePrinter() {
       windowsname: form.value.machinenumber || null,
       hostname: form.value.hostname || null,
       serialnumber: form.value.serialnumber || null,
+      gaugelabreference: form.value.gaugelabreference || null,
+      maintenancereference: form.value.maintenancereference || null,
       printertypeid: form.value.machinetypeid || null,
       statusid: form.value.statusid || null,
       vendorid: form.value.vendorid || null,