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).

docker/php/entrypoint.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+set -eu
+# Image and Compose both select www-data; validation and FPM inherit this identity.
+if [ "$1" = "php-fpm" ]; then
+    if [ "$(id -u)" = 0 ]; then
+        echo 'Refusing to validate or serve FPM as root; use www-data.' >&2
+        exit 1
+    fi
+    php /var/www/html/bin/check-config.php
+fi
+exec docker-php-entrypoint "$@"