fix: bake schema.sql into db image to fix Coolify bind mount error

Bind mount ./schema.sql created a directory instead of file in Coolify,
causing MySQL batch_readline error. Use Dockerfile.db to COPY schema
directly into the image instead.

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

Dockerfile.db

@@ -0,0 +1,2 @@
+FROM mysql:8.0
+COPY schema.sql /docker-entrypoint-initdb.d/schema.sql

docker-compose.yaml

@@ -24,7 +24,9 @@ services:
       start_period: 30s
 
   db:
-    image: mysql:8.0
+    build:
+      context: .
+      dockerfile: Dockerfile.db
     restart: unless-stopped
     environment:
       MYSQL_DATABASE: "${DB_NAME:-webgis_jalan}"
@@ -33,7 +35,6 @@ services:
       MYSQL_ROOT_PASSWORD: "${DB_ROOT_PASSWORD:?Set DB_ROOT_PASSWORD in Coolify}"
     volumes:
       - mysql-data:/var/lib/mysql
-      - ./schema.sql:/docker-entrypoint-initdb.d/schema.sql:ro
     healthcheck:
       test: ["CMD-SHELL", "mysqladmin ping -h localhost -uroot -p\"$${MYSQL_ROOT_PASSWORD}\" --silent"]
       interval: 5s