feat(auth): Implement sign-in UI and logic

- Added email/password sign-in
- Implemented Google sign-in
- Added anonymous sign-in
- Displayed loading indicator
- Showed error messages

Author: fulleni

lib/authentication/view/authentication_page.dart

@@ -12,18 +12,101 @@ class AuthenticationPage extends StatelessWidget {
       create: (context) => AuthenticationBloc(
         authenticationRepository: context.read<HtAuthenticationRepository>(),
       ),
-      child: const _AuthenticationView(),
+      child:  _AuthenticationView(),
     );
   }
 }
 
 class _AuthenticationView extends StatelessWidget {
-  const _AuthenticationView();
+  _AuthenticationView();
+
+    final _emailController = TextEditingController();
+    final _passwordController = TextEditingController();
 
   @override
   Widget build(BuildContext context) {
-    return const Placeholder(
-      child: Text('AUTHENTICATION PAGE'),
+
+    return Scaffold(
+      body: SafeArea(
+        child: BlocBuilder<AuthenticationBloc, AuthenticationState>(
+          builder: (context, state) {
+            if (state is AuthenticationLoading) {
+              return const Center(child: CircularProgressIndicator());
+            }
+            if (state is AuthenticationFailure) {
+              WidgetsBinding.instance.addPostFrameCallback((_) {
+                ScaffoldMessenger.of(context).showSnackBar(
+                  SnackBar(content: Text(state.errorMessage)),
+                );
+              });
+            }
+            return Padding(
+              padding: const EdgeInsets.all(16),
+              child: Column(
+                mainAxisAlignment: MainAxisAlignment.center,
+                children: [
+                  const Text(
+                    'Sign In',
+                    style: TextStyle(fontSize: 24, fontWeight: FontWeight.bold),
+                  ),
+                  const SizedBox(height: 32),
+                  TextFormField(
+                    controller: _emailController,
+                    decoration: const InputDecoration(
+                      labelText: 'Email',
+                      border: OutlineInputBorder(),
+                    ),
+                    keyboardType: TextInputType.emailAddress,
+                  ),
+                  const SizedBox(height: 16),
+                  TextFormField(
+                    controller: _passwordController,
+                    decoration: const InputDecoration(
+                      labelText: 'Password',
+                      border: OutlineInputBorder(),
+                    ),
+                    obscureText: true,
+                  ),
+                  const SizedBox(height: 32),
+                  ElevatedButton(
+                    onPressed: () {
+                      context.read<AuthenticationBloc>().add(
+                            AuthenticationEmailSignInRequested(
+                              email: _emailController.text,
+                              password: _passwordController.text,
+                            ),
+                          );
+                    },
+                    child: const Text('Sign In with Email'),
+                  ),
+                  const SizedBox(height: 16),
+                  ElevatedButton(
+                    onPressed: () {
+                      context
+                          .read<AuthenticationBloc>()
+                          .add(const AuthenticationGoogleSignInRequested());
+                    },
+                    style: ElevatedButton.styleFrom(
+                      backgroundColor: Colors.white,
+                      foregroundColor: Colors.black,
+                    ),
+                    child: const Text('Sign In with Google'),
+                  ),
+                  const SizedBox(height: 16),
+                  ElevatedButton(
+                    onPressed: () {
+                      context
+                          .read<AuthenticationBloc>()
+                          .add(const AuthenticationAnonymousSignInRequested());
+                    },
+                    child: const Text('Sign In Anonymously'),
+                  ),
+                ],
+              ),
+            );
+          },
+        ),
+      ),
     );
   }
 }