feat: add Docker setup exposing app on port 7876

- Dockerfile: php:apache base, installs PHP extensions + Composer,
  configures Apache to listen on port 7876, bundles app code,
  runs composer install at build time
- docker-compose.yml: web service (port 7876) + MariaDB LTS with
  healthcheck; writable volume for DB persistence
- docker/entrypoint.sh: generates .env from environment variables
  at container start, fixes runtime permissions
- docker/php.ini: tuned PHP limits (512M memory, 32M upload)
- .dockerignore: excludes .git, vendor, logs, cache, old docker dir
- .env.example: template for required environment variables

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.example

@@ -0,0 +1,12 @@
+# Copy to .env and fill in real values before running docker compose up
+
+DB_DATABASE=domain_monitor
+DB_USERNAME=domain_monitor
+DB_PASSWORD=changeme
+DB_ROOT_PASSWORD=rootchangeme
+
+# Timezone (e.g. Europe/Bucharest)
+TZ=UTC
+
+# Set to 'development' to show detailed error pages
+APP_ENV=production