refactor(error-ui): mask error message, center error, drop test buttons

- Show a generic "we're aware and are working on a fix" message in the
  shared ErrorBoundary instead of the raw error text (still logged and
  reported to PostHog).
- Vertically center the dashboard route error (min-h-svh), matching the
  app-level error boundary.
- Remove the temporary PostHog error-tracking validation buttons now that
  error tracking is verified.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: huv1k

src/features/dashboard/shared/route-error.tsx

@@ -34,6 +34,7 @@ export function DashboardRouteError({
   return (
     <ErrorBoundary
       description="Sorry, something went wrong with this page."
+      className="min-h-svh"
       error={error}
       onRetry={() => {
         router.refresh()

src/features/dashboard/sidebar/footer.tsx

@@ -24,20 +24,13 @@ import {
 } from '@/ui/primitives/sidebar'
 import DashboardSurveyPopover from '../navbar/dashboard-survey-popover'
 import ContactSupportDialog from '../navbar/report-issue-dialog'
-import {
-  RenderErrorTestButton,
-  ThrowErrorTestButton,
-} from './throw-error-test-button'
 
 export default function DashboardSidebarFooter() {
   return (
     <>
       <SidebarFooter>
         <SidebarGroup className="!p-0">
           <SidebarMenu>
-            {/* TEMPORARY: PostHog error-tracking validation (ENG-4261). Remove later. */}
-            <ThrowErrorTestButton />
-            <RenderErrorTestButton />
             <SidebarMenuItem key="github">
               <SidebarMenuButton asChild tooltip="GitHub">
                 <Link

src/features/dashboard/sidebar/throw-error-test-button.tsx

@@ -8,6 +8,11 @@ import { cn } from '@/lib/utils'
 import { ErrorIndicator } from './error-indicator'
 import Frame from './frame'
 
+// User-facing message shown in place of the raw error. The underlying error is
+// still logged and reported to PostHog, so we don't expose internals to users.
+const GENERIC_ERROR_MESSAGE =
+  "We're aware of the issue and are working to fix it as soon as possible."
+
 export default function ErrorBoundary({
   error,
   description,
@@ -48,7 +53,7 @@ export default function ErrorBoundary({
       {hideFrame ? (
         <ErrorIndicator
           description={description}
-          message={error.message}
+          message={GENERIC_ERROR_MESSAGE}
           className="border-none"
           onRetry={onRetry}
         />