feat(auth, ui): add Keycloak login flow and enhance LoginScreen UI

- Introduced `onKeycloakLogin` callback in LoginScreen for Keycloak-based authentication.
- Updated Login UI with "Login with Keycloak" button and loading indicator for OIDC flow.
- Implemented dividers and spacing for improved visual structure.

- Refactored LandingScreen into a separate file for better modularity and maintenance.
- Reintroduced LandingScreen features, hero section, and footer with enhanced composables.

- Added `composeHotReload` plugin and `uiTooling` dependency for development improvements.

Signed-off-by: Stefan Mogeritsch <stefan.mo.co@gmail.com>

frontend/core/auth/src/commonMain/kotlin/at/mocode/frontend/core/auth/presentation/LoginScreen.kt

@@ -70,7 +70,8 @@ fun LoginScreen(
           focusManager = focusManager,
           onUsernameChange = viewModel::updateUsername,
           onPasswordChange = viewModel::updatePassword,
-          onLogin = { focusManager.clearFocus(); viewModel.login() }
+          onLogin = { focusManager.clearFocus(); viewModel.login() },
+          onKeycloakLogin = viewModel::startOidcFlow
         )
       } else {
         RegisterTabContent()
@@ -91,7 +92,8 @@ private fun LoginTabContent(
   focusManager: androidx.compose.ui.focus.FocusManager,
   onUsernameChange: (String) -> Unit,
   onPasswordChange: (String) -> Unit,
-  onLogin: () -> Unit
+  onLogin: () -> Unit,
+  onKeycloakLogin: () -> Unit = {},
 ) {
   var passwordVisible by remember { mutableStateOf(false) }
 
@@ -169,6 +171,34 @@ private fun LoginTabContent(
       }
     }
 
+    Row(
+      modifier = Modifier.fillMaxWidth().padding(vertical = 16.dp),
+      verticalAlignment = Alignment.CenterVertically
+    ) {
+      HorizontalDivider(modifier = Modifier.weight(1f))
+      Text(
+        text = "  oder  ",
+        style = MaterialTheme.typography.bodySmall,
+        color = MaterialTheme.colorScheme.onSurfaceVariant
+      )
+      HorizontalDivider(modifier = Modifier.weight(1f))
+    }
+
+    OutlinedButton(
+      onClick = onKeycloakLogin,
+      enabled = !uiState.isLoading && !uiState.isOidcLoading,
+      modifier = Modifier.fillMaxWidth().height(48.dp)
+    ) {
+      if (uiState.isOidcLoading) {
+        CircularProgressIndicator(
+          modifier = Modifier.size(20.dp),
+          strokeWidth = 2.dp
+        )
+      } else {
+        Text("Mit Keycloak anmelden")
+      }
+    }
+
   }
 }