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>

lib/auth.ts

@@ -196,9 +196,9 @@ if (typeof window === 'undefined') {
   }, 60000); // Clear every minute
 }
 
-export function checkRateLimit(ip: string, maxRequests: number = 10, windowMs: number = 60000): boolean {
+export function checkRateLimit(ip: string, maxRequests: number = 10, windowMs: number = 60000, prefix: string = 'admin'): boolean {
   const now = Date.now();
-  const key = `admin_${ip}`;
+  const key = `${prefix}_${ip}`;
   
   const current = rateLimitMap.get(key);
   
@@ -215,8 +215,8 @@ export function checkRateLimit(ip: string, maxRequests: number = 10, windowMs: n
   return true;
 }
 
-export function getRateLimitHeaders(ip: string, maxRequests: number = 10, windowMs: number = 60000): Record<string, string> {
-  const current = rateLimitMap.get(`admin_${ip}`);
+export function getRateLimitHeaders(ip: string, maxRequests: number = 10, windowMs: number = 60000, prefix: string = 'admin'): Record<string, string> {
+  const current = rateLimitMap.get(`${prefix}_${ip}`);
   const remaining = current ? Math.max(0, maxRequests - current.count) : maxRequests;
   
   return {