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/dashboard/FilterBar.tsx

@@ -29,7 +29,7 @@ export default function FilterBar({ filters, onRemove, onClear }: FilterBarProps
       {filters.length > 1 && (
         <button
           onClick={onClear}
-          className="px-2 py-1.5 text-xs font-medium text-neutral-500 dark:text-neutral-400 hover:text-neutral-900 dark:hover:text-white transition-colors cursor-pointer"
+          className="px-2 py-1.5 text-xs font-medium text-neutral-400 hover:text-neutral-900 dark:hover:text-white transition-colors cursor-pointer"
         >
           Clear all
         </button>