Fix TypeScript type error in demo page - change project IDs from number to string

Changed all project IDs in mock data from numeric type (1, 2, 3, 4) to string type ('1', '2', '3', '4') to match the OffsetProject interface which expects string IDs.

This resolves the Docker build error:
Type 'number' is not assignable to type 'string' at line 312

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/checkout/success/demo/page.tsx

@@ -26,7 +26,7 @@ const mockOrderDetails = {
       description: 'Curated mix of high-impact verified carbon offset projects',
       projects: [
         {
-          id: 1,
+          id: '1',
           name: 'Rimba Raya Biodiversity Reserve',
           type: 'Forestry',
           description: 'Protecting 64,000 hectares of tropical peat swamp forest in Borneo',
@@ -41,7 +41,7 @@ const mockOrderDetails = {
           }
         },
         {
-          id: 2,
+          id: '2',
           name: 'Verified Blue Carbon',
           type: 'Blue Carbon',
           description: 'Coastal wetland restoration for carbon sequestration',
@@ -56,7 +56,7 @@ const mockOrderDetails = {
           }
         },
         {
-          id: 3,
+          id: '3',
           name: 'Direct Air Capture Technology',
           type: 'Direct Air Capture',
           description: 'Advanced technology removing CO2 directly from atmosphere',
@@ -71,7 +71,7 @@ const mockOrderDetails = {
           }
         },
         {
-          id: 4,
+          id: '4',
           name: 'Renewable Energy Development',
           type: 'Renewable Energy',
           description: 'Wind and solar power generation replacing fossil fuels',