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)

app/sites/[id]/funnels/page.tsx

@@ -40,7 +40,7 @@ export default function FunnelsPage() {
       <div className="mb-8">
         <div className="flex items-center justify-between mb-6">
           <div>
-            <h1 className="text-2xl font-bold text-neutral-900 dark:text-white">
+            <h1 className="text-2xl font-bold text-white">
               Funnels
             </h1>
             <p className="text-neutral-600 dark:text-neutral-400">
@@ -65,7 +65,7 @@ export default function FunnelsPage() {
               className="mb-6"
               unoptimized
             />
-            <h3 className="text-lg font-semibold text-neutral-900 dark:text-white mb-2">
+            <h3 className="text-lg font-semibold text-white mb-2">
               No funnels yet
             </h3>
             <p className="text-neutral-600 dark:text-neutral-400 mb-6 max-w-md mx-auto">
@@ -89,7 +89,7 @@ export default function FunnelsPage() {
                 <div className="bg-white dark:bg-neutral-900 border border-neutral-200 dark:border-neutral-800 rounded-2xl p-6 hover:border-brand-orange/50 transition-colors">
                   <div className="flex items-center justify-between">
                     <div>
-                      <h3 className="text-xl font-bold text-neutral-900 dark:text-white group-hover:text-brand-orange transition-colors">
+                      <h3 className="text-xl font-bold text-white group-hover:text-brand-orange transition-colors">
                         {funnel.name}
                       </h3>
                       {funnel.description && (