Add photo management for models and employees; fix stale detail navigation

Model photos: upload/replace/delete on /api/models/<id>/image (admin),
stored under instance/modelimages/ with a public serve route; thumbnail
plus Upload/Replace/Remove controls in the Models settings modal; the
URL field remains as a manual alternative.

Employee photos, mode-aware: self-hosted directory employees get
upload/replace/delete (photo-<sso> under instance/employeephotos/,
employees plugin migration 0002); external directory mode passes the
HR-supplied picture URL through read-only (writes 409). One resolver
feeds both consumers - the shopfloor recognition/recert kiosk cards and
the employee detail hero - in either mode.

Navigation fix: router-view is keyed on route path, so following a
relationship link between two assets of the same type (machine ->
dualpath machine) reloads the page instead of showing stale content;
query-only URL changes still avoid a remount.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/views/employees/EmployeeDetail.vue

@@ -5,8 +5,8 @@
 
     <template v-else-if="employee">
       <div class="hero-card">
-        <div class="hero-image" v-if="employee.Picture">
-          <img :src="employee.Picture" :alt="fullName" />
+        <div class="hero-image" v-if="employee.photourl">
+          <img :src="employee.photourl" :alt="fullName" />
         </div>
         <div class="hero-image placeholder" v-else>
           <span class="initials">{{ initials }}</span>