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>

docker-compose.yml

@@ -0,0 +1,43 @@
+services:
+  web:
+    build: .
+    container_name: domnitor-web
+    restart: unless-stopped
+    ports:
+      - "7876:7876"
+    environment:
+      DB_HOST: db
+      DB_PORT: "3306"
+      DB_DATABASE: ${DB_DATABASE:-domain_monitor}
+      DB_USERNAME: ${DB_USERNAME:-domain_monitor}
+      DB_PASSWORD: ${DB_PASSWORD:-changeme}
+      APP_ENV: ${APP_ENV:-production}
+      TZ: ${TZ:-UTC}
+    depends_on:
+      db:
+        condition: service_healthy
+
+  db:
+    image: mariadb:lts
+    container_name: domnitor-db
+    restart: unless-stopped
+    environment:
+      MARIADB_DATABASE: ${DB_DATABASE:-domain_monitor}
+      MARIADB_USER: ${DB_USERNAME:-domain_monitor}
+      MARIADB_PASSWORD: ${DB_PASSWORD:-changeme}
+      MARIADB_ROOT_PASSWORD: ${DB_ROOT_PASSWORD:-rootchangeme}
+      TZ: ${TZ:-UTC}
+    command:
+      - "--character-set-server=utf8mb4"
+      - "--collation-server=utf8mb4_unicode_ci"
+    volumes:
+      - dbdata:/var/lib/mysql
+    healthcheck:
+      test: ["CMD", "healthcheck.sh", "--connect", "--innodb_initialized"]
+      start_period: 15s
+      interval: 10s
+      timeout: 5s
+      retries: 5
+
+volumes:
+  dbdata: