fix: frontend consistency audit — 55 files cleaned up

Consistency fixes:
- Extract getThisWeekRange/getThisMonthRange to shared lib/utils/dateRanges.ts
  (removed 4 identical copy-pasted definitions)
- Add error boundaries for behavior, cdn, search, pagespeed pages
  (4 new error.tsx files — previously fell through to generic parent error)
- Add "View setup guide" CTA to empty states on journeys and behavior pages
  (previously showed text with no actionable button)
- Fix non-lazy useState initializer in funnel detail page
- Fix Bot & Spam settings header from text-xl to text-2xl (matches all other sections)
- Add useMinimumLoading to PageSpeed skeleton (consistent with all other pages)

Cleanup:
- Remove 438 redundant dark: class prefixes (app is dark-mode only)
  text-neutral-500 dark:text-neutral-400 → text-neutral-400 (206 occurrences)
  text-neutral-900 dark:text-white → text-white (232 occurrences)
- Remove dead @stripe/react-stripe-js and @stripe/stripe-js packages
  (billing migrated to Polar, no code imports Stripe)
- Remove duplicate motion package (framer-motion is the one actually used)

components/funnels/FunnelForm.tsx

@@ -206,7 +206,7 @@ export default function FunnelForm({ siteId, initialData, onSubmit, submitLabel,
           Back to Funnels
         </Link>
 
-        <h1 className="text-2xl font-bold text-neutral-900 dark:text-white mb-2">
+        <h1 className="text-2xl font-bold text-white mb-2">
           {initialData ? 'Edit Funnel' : 'Create New Funnel'}
         </h1>
         <p className="text-neutral-600 dark:text-neutral-400">
@@ -252,7 +252,7 @@ export default function FunnelForm({ siteId, initialData, onSubmit, submitLabel,
         {/* Steps */}
         <div className="space-y-4 mb-6">
           <div className="flex items-center justify-between">
-            <h3 className="text-lg font-semibold text-neutral-900 dark:text-white">
+            <h3 className="text-lg font-semibold text-white">
               Funnel Steps
             </h3>
           </div>