refactor: rename features to room-based directory structure

- Rename features/dashboard → features/front_hall
- Update routes: /, /control-room, /parlor, /settings
- Update navigation to 4 rooms (removed chat tab - will be omnipresent dock)
- Add docs/UI_LAYOUT.md with wireframes and responsive specs
- Update ARCHITECTURE.md and PLAN.md to reflect room structure

Directory structure now mirrors "Rooms of the Estate" UI navigation:
- front_hall/ (dashboard)
- control_room/ (infrastructure - containers, stacks, etc.)
- parlor/ (home automation)
- library/ (future)
- study/ (future, hidden)

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/features/front_hall/presentation/pages/front_hall_page.dart

@@ -2,9 +2,9 @@ import 'package:flutter/material.dart';
 
 import '../../../../version.g.dart';
 
-/// Dashboard home page - overview of the homelab.
-class DashboardPage extends StatelessWidget {
-  const DashboardPage({super.key});
+/// Front Hall - estate overview and quick access.
+class FrontHallPage extends StatelessWidget {
+  const FrontHallPage({super.key});
 
   @override
   Widget build(BuildContext context) {
@@ -12,7 +12,7 @@ class DashboardPage extends StatelessWidget {
 
     return Scaffold(
       appBar: AppBar(
-        title: const Text('Dashboard'),
+        title: const Text('Front Hall'),
         actions: [
           IconButton(
             icon: const Icon(Icons.refresh),