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/api/n8n/hardcover/currently-reading/route.ts

@@ -21,7 +21,7 @@ export async function GET(request: NextRequest) {
       : ip;
   const maxPerMinute = process.env.NODE_ENV === "development" ? 60 : 10;
 
-  if (!checkRateLimit(rateKey, maxPerMinute, 60000)) { // requests per minute
+  if (!checkRateLimit(rateKey, maxPerMinute, 60000, 'n8n-reading')) { // requests per minute
     return NextResponse.json(
       { error: 'Rate limit exceeded. Please try again later.' },
       { status: 429 }

app/api/n8n/status/route.ts

@@ -20,7 +20,7 @@ export async function GET(request: NextRequest) {
       : ip;
   const maxPerMinute = process.env.NODE_ENV === "development" ? 300 : 30;
 
-  if (!checkRateLimit(rateKey, maxPerMinute, 60000)) { // requests per minute
+  if (!checkRateLimit(rateKey, maxPerMinute, 60000, 'n8n-status')) { // requests per minute
     return NextResponse.json(
       { error: 'Rate limit exceeded. Please try again later.' },
       { status: 429 }