fix: add missing transcription entry to PANEL_DIMENSIONS

BasePanel reads PANEL_DIMENSIONS[currentPanelType] to get the panel
dimensions (topOffset, bottomOffset, width). The transcription panel
type was added to the panel list and render switch during CIS Phase 3C
but was never added to PANEL_DIMENSIONS. This caused a crash whenever
the BasePanel rendered with the transcription tab active:

  PANEL_DIMENSIONS["transcription"] === undefined
  undefined.topOffset → TypeError: Cannot read properties of undefined

This crash appeared as a topOffset error anywhere a Tldraw canvas was
rendered (singlePlayerPage, multiplayerUser, etc.).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/utils/tldraw/ui-overrides/components/shared/panel-styles.ts

@@ -44,6 +44,11 @@ export const PANEL_DIMENSIONS = {
     topOffset: `0px`,
     bottomOffset: '0px',
   },
+  'transcription': {
+    width: '300px',
+    topOffset: `0px`,
+    bottomOffset: '0px',
+  },
   'search': {
     width: '300px',
     topOffset: `0px`,