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_merchants.sql

@@ -0,0 +1,17 @@
+-- Create merchants table
+CREATE TABLE merchants (
+    id UUID DEFAULT gen_random_uuid() PRIMARY KEY,
+    name TEXT NOT NULL,
+    api_key TEXT UNIQUE DEFAULT encode(gen_random_bytes(32), 'hex'),
+    webhook_url TEXT,
+    created_at TIMESTAMPTZ DEFAULT NOW()
+);
+
+-- Add merchant_id to transactions
+ALTER TABLE transactions ADD COLUMN merchant_id UUID REFERENCES merchants(id);
+
+-- Update RLS for transactions to support merchants (future proofing)
+-- For now, we'll just keep the admin policy as is, but we'll add more later.
+
+-- Optional: Add index for performance
+CREATE INDEX idx_transactions_merchant_id ON transactions(merchant_id);