feat(01-01): Initialize Supabase in main.dart

- Updated main.dart with proper Supabase initialization
- Added environment loading with error handling
- Replaced default Flutter template with Sage app
- Created simple HomePage with Supabase connection status
- Used debugPrint instead of print for production compliance

lib/main.dart

@@ -0,0 +1,86 @@
+import 'package:flutter/material.dart';
+import 'package:supabase_flutter/supabase_flutter.dart';
+import 'package:flutter_dotenv/flutter_dotenv.dart';
+import 'core/constants/supabase_constants.dart';
+
+void main() async {
+  WidgetsFlutterBinding.ensureInitialized();
+  
+  try {
+    // Load environment variables
+    await SupabaseConstants.initialize();
+    
+    // Initialize Supabase
+    await Supabase.initialize(
+      url: SupabaseConstants.supabaseUrl,
+      anonKey: SupabaseConstants.supabaseAnonKey,
+    );
+    
+    debugPrint('Supabase initialized successfully');
+  } catch (e) {
+    debugPrint('Failed to initialize Supabase: $e');
+  }
+  
+  runApp(const SageApp());
+}
+
+class SageApp extends StatelessWidget {
+  const SageApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      title: 'Sage - Food Inventory Tracker',
+      theme: ThemeData(
+        colorScheme: ColorScheme.fromSeed(seedColor: Colors.green),
+        useMaterial3: true,
+      ),
+      home: const HomePage(),
+    );
+  }
+}
+
+class HomePage extends StatelessWidget {
+  const HomePage({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
+        title: const Text('Sage'),
+      ),
+      body: const Center(
+        child: Column(
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: [
+            Text(
+              'Welcome to Sage',
+              style: TextStyle(
+                fontSize: 24,
+                fontWeight: FontWeight.bold,
+              ),
+            ),
+            SizedBox(height: 16),
+            Text(
+              'Your collaborative household food inventory tracker',
+              style: TextStyle(
+                fontSize: 16,
+                color: Colors.grey,
+              ),
+            ),
+            SizedBox(height: 32),
+            Text(
+              'Supabase connection: ✓ Ready',
+              style: TextStyle(
+                fontSize: 14,
+                color: Colors.green,
+                fontWeight: FontWeight.w500,
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}