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/network/NetworkDeviceDetail.vue

@@ -111,6 +111,14 @@
               <span class="info-label">Serial Number</span>
               <span class="info-value mono">{{ device.serialnumber || '-' }}</span>
             </div>
+            <div class="info-row" v-if="isEnabled('gaugelabreference', 'network_device') && device.gaugelabreference">
+              <span class="info-label">Gauge Lab Reference</span>
+              <span class="info-value mono">{{ device.gaugelabreference }}</span>
+            </div>
+            <div class="info-row" v-if="isEnabled('maintenancereference', 'network_device') && device.maintenancereference">
+              <span class="info-label">Maintenance Reference</span>
+              <span class="info-value mono">{{ device.maintenancereference }}</span>
+            </div>
             <div class="info-row">
               <span class="info-label">Vendor</span>
               <span class="info-value">{{ device.networkdevice?.vendorname || '-' }}</span>
@@ -181,6 +189,9 @@ import { Network, Router, Shield, Wifi, Camera, Server, Server as Rack, Globe }
 import { useAuthStore } from '../../stores/auth'
 import { networkApi } from '../../api'
 import AssetRelationships from '../../components/AssetRelationships.vue'
+import { useIdentifierFlags } from '../../composables/identifierSettings'
+
+const { isEnabled } = useIdentifierFlags()
 
 const route = useRoute()
 const router = useRouter()