feat: implement merchant dashboard, secure auth, and short_id system

- Added dedicated merchant dashboard with analytics and transactions
- Implemented API Key based authentication for merchants
- Introduced 8-character Short IDs for merchants to use in URLs
- Refactored checkout and payment intent APIs to support multi-gateway
- Enhanced Landing Page with Merchant Portal access and marketing copy
- Fixed Next.js 15 async params build issues
- Updated internal branding to P2CGateway
- Added AyrisTech credits to footer

docs/update_schema_providers.sql

@@ -0,0 +1,11 @@
+-- Add payment provider configuration to merchants table
+ALTER TABLE merchants ADD COLUMN payment_provider TEXT NOT NULL DEFAULT 'stripe';
+ALTER TABLE merchants ADD COLUMN provider_config JSONB DEFAULT '{}'::jsonb;
+
+-- Add provider info to transactions to track which one was used
+ALTER TABLE transactions ADD COLUMN provider TEXT NOT NULL DEFAULT 'stripe';
+ALTER TABLE transactions ADD COLUMN provider_tx_id TEXT;
+ALTER TABLE transactions ADD COLUMN provider_status TEXT;
+
+-- Update status constraint if needed (ours was already quite flexible, but let's be sure)
+-- Currently: CHECK (status IN ('pending', 'succeeded', 'failed'))