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).

public/index.php

@@ -0,0 +1,32 @@
+<?php
+
+declare(strict_types=1);
+
+// This boundary intentionally does not depend on autoloading, DI or templates.
+ini_set('display_errors', '0');
+$stage = 'autoload';
+try {
+    require dirname(__DIR__) . '/vendor/autoload.php';
+    $stage = 'configuration';
+    $config = \MeshVault\Config\AppConfig::fromEnvironment(getenv());
+    $stage = 'application';
+    \MeshVault\Http\AppFactory::create($config)->run();
+} catch (\Throwable $exception) {
+    $safeDetail = $stage === 'configuration' && $exception instanceof \InvalidArgumentException
+        ? $exception->getMessage()
+        : 'Check dependencies and application bootstrap at ' . $exception->getFile() . ':' . $exception->getLine();
+    error_log((string) json_encode([
+        'message' => 'Application bootstrap failed',
+        'stage' => $stage,
+        'detail' => $safeDetail,
+        'exception_type' => $exception::class,
+    ], JSON_UNESCAPED_SLASHES | JSON_INVALID_UTF8_SUBSTITUTE));
+    http_response_code(500);
+    header('Content-Type: text/html; charset=utf-8');
+    echo '<!doctype html><html lang="en"><meta charset="utf-8"><title>Internal Server Error</title>';
+    echo '<h1>Internal Server Error</h1>';
+    if (getenv('MESHVAULT_ENV') === 'development') {
+        echo '<pre>' . htmlspecialchars($safeDetail, ENT_QUOTES | ENT_SUBSTITUTE, 'UTF-8') . '</pre>';
+    }
+    echo '</html>';
+}