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>

docs/BACKUP-RESTORE.md

@@ -18,6 +18,8 @@ app pointing at floor plans and logos that no longer exist.
 |------|----------|-----|
 | Database | MySQL `shopdb_flask` | All application data. |
 | `instance/branding/` | repo `instance/` dir | Uploaded logos and favicon. |
+| `instance/modelimages/` | repo `instance/` dir | Uploaded vendor-model photos. |
+| `instance/employeephotos/` | repo `instance/` dir | Uploaded self-hosted employee photos (external mode serves photos from the HR database instead). |
 | `instance/` floor plans | repo `instance/` dir | Uploaded map blueprints. |
 | `instance/plugins.json` | repo `instance/` dir | Which plugins this site enabled. |
 | `.env` | repo root (offline, secured) | Secrets needed to bring the stack back up. Store separately from the data backup, in a secrets manager. |