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).

composer.json

@@ -4,14 +4,30 @@
     "type": "project",
     "license": "AGPL-3.0-only",
     "require": {
-        "php": ">=8.3"
+        "php": ">=8.3",
+        "monolog/monolog": "^3.12",
+        "php-di/php-di": "^7.1",
+        "psr/log": "^3.0",
+        "slim/psr7": "^1.8",
+        "slim/slim": "^4.15.3"
     },
     "require-dev": {
+        "phpunit/phpunit": "^12.0",
         "squizlabs/php_codesniffer": "^3.13.5"
     },
+    "autoload": {
+        "psr-4": {
+            "MeshVault\\": "src/"
+        }
+    },
+    "autoload-dev": {
+        "psr-4": {
+            "MeshVault\\Tests\\": "tests/"
+        }
+    },
     "scripts": {
         "lint": "phpcs --standard=phpcs.xml.dist",
-        "test": "@php tests/foundation.php"
+        "test": ["@php tests/foundation.php", "@php vendor/phpunit/phpunit/phpunit"]
     },
     "config": {
         "sort-packages": true,