fix: namespace rate limit buckets per endpoint, remove custom analytics

- Add `prefix` param to checkRateLimit/getRateLimitHeaders so each endpoint
  has its own bucket (previously all shared `admin_${ip}`, causing 429s when
  analytics/track incremented past n8n endpoints' lower limits)
- n8n/hardcover/currently-reading → prefix 'n8n-reading'
- n8n/status → prefix 'n8n-status'
- analytics/track → prefix 'analytics-track'
- Remove custom analytics system (AnalyticsProvider, lib/analytics,
  lib/useWebVitals, all /api/analytics/* routes) — was causing 500s in
  production due to missing PostgreSQL PageView table
- Remove analytics consent toggle from ConsentBanner/ConsentProvider

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

app/components/ConsentProvider.tsx

@@ -3,7 +3,6 @@
 import React, { createContext, useCallback, useContext, useEffect, useMemo, useState } from "react";
 
 export type ConsentState = {
-  analytics: boolean;
   chat: boolean;
 };
 
@@ -20,7 +19,6 @@ function readConsentFromCookie(): ConsentState | null {
   try {
     const parsed = JSON.parse(value) as Partial<ConsentState>;
     return {
-      analytics: !!parsed.analytics,
       chat: !!parsed.chat,
     };
   } catch {