v0.2.3: visible cross-panel drag ghost, front-image fallback, shorter hint

- Fix invisible device while dragging from front to rear: the block
  being dragged stayed structurally inside its own source <svg>, so it
  rendered underneath the other panel once it visually overlapped it.
  Replaced the in-SVG transform with a free-floating HTML ghost fixed
  to <body> that tracks the pointer, unaffected by either SVG's own
  stacking - the original block just dims in place during the drag, as
  before.
- Fix rear elevation showing nothing for a device type with no
  rear_image: only full-depth devices (which have a genuinely
  different back) are restricted to their own rear image now; a
  shallow device (e.g. a PDU) falls back to its front image on the
  rear view, since that's usually the only picture that exists and is
  still recognisable either way.
- Shorten the drag-hint badge text; the German translation of the
  previous, longer wording didn't fit well next to the other controls
  above the elevation.

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

netbox_rack_concept/locale/de/LC_MESSAGES/django.po

@@ -924,7 +924,5 @@ msgid_plural "{{ counter }} planned devices will be created per rack."
 msgstr[0] "Pro Rack wird {{ counter }} geplantes Gerät angelegt."
 msgstr[1] "Pro Rack werden {{ counter }} geplante Geräte angelegt."
 
-msgid "Drag devices to move or flip them between front and rear"
-msgstr ""
-"Geräte ziehen, um sie zu verschieben oder zwischen Front und Rückseite zu "
-"wechseln"
+msgid "Drag to move or flip sides"
+msgstr "Ziehen zum Verschieben/Wechseln"