Move application install tracking off Machine onto Computer

- applications.py installed-on + per-computer install/uninstall/update endpoints
  now use Computer / ComputerInstalledApp instead of Machine / InstalledApp.
- ApplicationDetail "Installed On" list reads the computer shape.
- Drop the unused Machine/MachineType import from the assets map endpoint.

No active core endpoint uses the Machine model anymore (only the legacy
/api/machines blueprint and reference-data seeder remain).

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

frontend/src/views/applications/ApplicationDetail.vue

@@ -100,12 +100,12 @@
               <router-link
                 v-for="install in installedOn"
                 :key="install.id"
-                :to="`/pcs/${install.machineid}`"
+                :to="`/pcs/${install.computerid}`"
                 class="pc-item"
               >
                 <div class="pc-info">
-                  <span class="pc-name">{{ install.machine?.machinenumber || `PC #${install.machineid}` }}</span>
-                  <span class="pc-alias" v-if="install.machine?.alias">{{ install.machine.alias }}</span>
+                  <span class="pc-name">{{ install.computer?.hostname || install.computer?.assetnumber || `PC #${install.computerid}` }}</span>
+                  <span class="pc-alias" v-if="install.computer?.assetnumber">{{ install.computer.assetnumber }}</span>
                 </div>
                 <div class="pc-version" v-if="install.version">
                   v{{ install.version }}