build: M1 Dockerized development stack with PHP skeleton, config/logging, Tailwind assets, and wrappers

Implements MeshVault M1 (issues #6–11):

- Four-service Docker Compose stack (nginx, PHP-FPM 8.3, PostgreSQL 17, Node assets)
- Slim 4 + PHP-DI routing with escaped PHP views and production/dev error handling
- Immutable validated AppConfig with redacted diagnostics
- JSON stdout Monolog logging with job-scoped context
- Tailwind CSS v4 deterministic locked builds with template scanning
- POSIX and PowerShell dev wrappers (up/down/test/lint/assets/watch)
- Startup config validation fails before FPM serves as unprivileged www-data
- migrate/seed explicitly unavailable until M2 (#12); #10 remains open

Verified via clean-start acceptance on remote host (keith@192.168.2.23).

src/Http/HomeHandler.php

@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MeshVault\Http;
+
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+
+final readonly class HomeHandler
+{
+    public function __construct(private View $view)
+    {
+    }
+
+    public function __invoke(ServerRequestInterface $request, ResponseInterface $response): ResponseInterface
+    {
+        $response->getBody()->write($this->view->render('home', ['title' => 'MeshVault']));
+        return $response->withHeader('Content-Type', 'text/html; charset=utf-8');
+    }
+}