Fix PC installed-applications rendering; minor UI cleanups

The PC detail Installed Applications section 500d and vanished on any
real PC: ComputerInstalledApp had no to_dict, so the endpoint errored
and the v-if hid the section. Added the serializer (curated version
wins over the raw collected string, app name + description included)
and aligned PCDetail to the flat payload; regression test added.

Also: employee detail skips its USB panels when the usb plugin is
disabled (was firing 404s), and the shopfloor kiosk header is now
light-on-dark for readability.

810 tests pass; PC 259 installed apps verified live.

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

plugins/computers/models/computer.py

@@ -183,6 +183,25 @@ class ComputerInstalledApp(db.Model):
         db.Index('idx_compapp_app', 'appid'),
     )
 
+    def to_dict(self):
+        # Curated AppVersion wins; else the raw collected version string.
+        version = None
+        if self.appversion is not None:
+            version = self.appversion.version
+        elif self.installedversion:
+            version = self.installedversion
+        return {
+            'id': self.id,
+            'computerid': self.computerid,
+            'appid': self.appid,
+            'appname': self.application.appname if self.application else None,
+            'appdescription': self.application.appdescription if self.application else None,
+            'appversionid': self.appversionid,
+            'installedversion': version,
+            'installeddate': self.installeddate.isoformat() + 'Z' if self.installeddate else None,
+            'isactive': self.isactive,
+        }
+
 
 class AccessProtocol(db.Model):
     """