Fix WORKDIR, rename DB to e_ticket, simplify purge_dev

- Add WORKDIR /app to dev and prod Dockerfiles
- Rename database from e-ticket to e_ticket (PostgreSQL compat)
- purge_dev: remove only containers and volumes, keep images

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker/php/dev/Dockerfile

@@ -24,3 +24,5 @@ RUN docker-php-ext-configure gd --with-freetype --with-jpeg \
 
 RUN pecl install redis imagick \
     && docker-php-ext-enable redis imagick
+
+WORKDIR /app

docker/php/prod/Dockerfile

@@ -28,3 +28,5 @@ RUN pecl install redis imagick \
 
 COPY php.ini /usr/local/etc/php/conf.d/app.ini
 COPY opcache.ini /usr/local/etc/php/conf.d/opcache.ini
+
+WORKDIR /app