feat: implement API usage tracking and admin dashboard

- Added database schema for API tracking system:
  * api_usage table - tracks all Google Search and Gemini AI calls
  * user_credits table - prepared for future credits system
  * admin_users table - controls admin dashboard access
- Created comprehensive tracking service (track-api-usage.ts):
  * trackApiUsage() - records API calls with success/failure
  * checkDailyLimit() - enforces 80 Google Search calls/day limit
  * getUserApiStats() - per-user statistics
  * getGlobalApiStats() - app-wide statistics (admin only)
  * checkIsAdmin() - server-side authorization
- Integrated tracking into discover-whiskybase.ts:
  * Pre-call limit checking with friendly error messages
  * Post-call usage tracking for success and failures
  * User authentication verification
- Built admin dashboard at /admin:
  * Global statistics cards (total, today, by API type)
  * Top 10 users by API usage
  * Recent activity log with 50 latest calls
  * Color-coded status indicators
  * Secure access with RLS policies
- Features:
  * Daily limit resets at midnight Europe/Berlin timezone
  * Graceful error handling (allows on tracking failure)
  * Comprehensive indexes for fast queries
  * Ready for future credits/monetization system

src/services/discover-whiskybase.ts

@@ -1,5 +1,9 @@
 'use server';
 
+import { trackApiUsage, checkDailyLimit } from './track-api-usage';
+import { createServerComponentClient } from '@supabase/auth-helpers-nextjs';
+import { cookies } from 'next/headers';
+
 /**
  * Service to discover a Whiskybase ID for a given bottle.
  * Uses Google Custom Search JSON API to search Google and extracts the ID from the first result.
@@ -24,6 +28,27 @@ export async function discoverWhiskybaseId(bottle: {
         };
     }
 
+    // Get current user for tracking
+    const supabase = createServerComponentClient({ cookies });
+    const { data: { user } } = await supabase.auth.getUser();
+
+    if (!user) {
+        return {
+            success: false,
+            error: 'Benutzer nicht authentifiziert.'
+        };
+    }
+
+    // Check daily limit before making API call
+    const limitCheck = await checkDailyLimit('google_search');
+    if (!limitCheck.allowed) {
+        return {
+            success: false,
+            error: `Tageslimit für Whiskybase-Suchen erreicht (${limitCheck.limit} pro Tag). Versuche es morgen erneut.`,
+            limitReached: true
+        };
+    }
+
     try {
         // Construct targeted search query
         const queryParts = [
@@ -46,9 +71,25 @@ export async function discoverWhiskybaseId(bottle: {
 
         if (data.error) {
             console.error('Google API Error Response:', data.error);
+            // Track failed API call
+            await trackApiUsage({
+                userId: user.id,
+                apiType: 'google_search',
+                endpoint: 'customsearch/v1',
+                success: false,
+                errorMessage: data.error.message
+            });
             throw new Error(data.error.message || 'Google API Error');
         }
 
+        // Track successful API call
+        await trackApiUsage({
+            userId: user.id,
+            apiType: 'google_search',
+            endpoint: 'customsearch/v1',
+            success: true
+        });
+
         if (!data.items || data.items.length === 0) {
             return {
                 success: false,
@@ -77,6 +118,16 @@ export async function discoverWhiskybaseId(bottle: {
         return { success: false, error: 'Konnte keine gültige Whiskybase-ID im Suchergebnis finden.' };
     } catch (error) {
         console.error('Whiskybase Discovery Error:', error);
+        // Track failed attempt (if not already tracked)
+        if (user) {
+            await trackApiUsage({
+                userId: user.id,
+                apiType: 'google_search',
+                endpoint: 'customsearch/v1',
+                success: false,
+                errorMessage: error instanceof Error ? error.message : 'Unknown error'
+            });
+        }
         return {
             success: false,
             error: error instanceof Error ? error.message : 'Fehler bei der Suche auf Whiskybase.'