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/Dockerfile

@@ -0,0 +1,20 @@
+FROM php:8.3-fpm-bookworm
+
+RUN apt-get update && apt-get install -y --no-install-recommends libonig-dev libxml2-dev unzip \
+    && docker-php-ext-install mbstring dom \
+    && rm -rf /var/lib/apt/lists/*
+COPY --from=composer:2 /usr/bin/composer /usr/local/bin/composer
+WORKDIR /var/www/html
+# Dependencies are Linux-native and rebuilt from the lock, never host-mounted.
+COPY composer.json composer.lock ./
+RUN composer install --no-interaction --prefer-dist --no-progress
+COPY bin ./bin
+COPY docker/php/entrypoint.sh /usr/local/bin/meshvault-entrypoint
+COPY docker/php/zz-meshvault.conf /usr/local/etc/php-fpm.d/zz-meshvault.conf
+RUN chmod 755 /usr/local/bin/meshvault-entrypoint
+RUN mkdir -p /var/www/html/.phpunit.cache && chown www-data:www-data /var/www/html/.phpunit.cache
+
+# The entire FPM process runs as the same identity used for library checks.
+USER www-data
+ENTRYPOINT ["meshvault-entrypoint"]
+CMD ["php-fpm"]