feat: implement real uptime monitoring, alerts, admin dashboard, billing & usage tracking

- Uptime service: real HTTP HEAD checks with response time tracking
- Alert engine: evaluates scan results, auto-resolves recovered alerts
- Notifications: Resend email + webhook delivery
- Admin dashboard: system stats, user CRUD, org management (role-protected)
- Billing: tier limits (free/starter/pro/enterprise), usage tracking API
- Competitor analysis: real Lighthouse comparison + response time
- Tests: 11 backend + 11 frontend = 22 total tests passing
- Database: added competitor_metrics, alert_configurations tables

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

website-monitoring-frontend/database-schema.sql

@@ -166,4 +166,41 @@ CREATE POLICY "Users can view uptime checks for their organization's websites" O
       JOIN users u ON w.organization_id = u.organization_id
       WHERE u.id = auth.uid()
     )
+  );
+
+-- Competitor metrics table
+CREATE TABLE IF NOT EXISTS competitor_metrics (
+  id uuid DEFAULT gen_random_uuid() PRIMARY KEY,
+  website_id uuid REFERENCES websites(id) ON DELETE CASCADE,
+  url text NOT NULL,
+  name text,
+  performance_score numeric,
+  seo_score numeric,
+  accessibility_score numeric,
+  best_practices_score numeric,
+  status_code integer,
+  response_time integer,
+  last_scanned_at timestamp with time zone DEFAULT now(),
+  created_at timestamp with time zone DEFAULT now(),
+  UNIQUE(website_id, url)
+);
+
+CREATE INDEX IF NOT EXISTS idx_competitor_metrics_website_id ON competitor_metrics(website_id);
+
+-- Alert configurations table (per-website thresholds)
+CREATE TABLE IF NOT EXISTS alert_configurations (
+  id uuid DEFAULT gen_random_uuid() PRIMARY KEY,
+  website_id uuid REFERENCES websites(id) ON DELETE CASCADE UNIQUE,
+  performance_threshold numeric DEFAULT 0.5,
+  seo_threshold numeric DEFAULT 0.5,
+  accessibility_threshold numeric DEFAULT 0.5,
+  uptime_threshold numeric DEFAULT 0.95,
+  email_enabled boolean DEFAULT true,
+  email_address text,
+  slack_enabled boolean DEFAULT false,
+  slack_webhook_url text,
+  alert_frequency text DEFAULT 'immediate',
+  created_at timestamp with time zone DEFAULT now(),
+  updated_at timestamp with time zone DEFAULT now()
+);
   );