feat(infra): add docker-compose for local MariaDB with Prisma schema init

Applies prisma/migrations/*/migration.sql on first container boot via a
sourced docker-entrypoint-initdb.d script, so a fresh container matches a
`prisma migrate deploy` run without needing shadow-database privileges.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docker/mariadb-initdb/10-apply-prisma-schema.sh

@@ -0,0 +1,10 @@
+# Sourced (non-executable) by mariadb-docker's entrypoint, which exposes
+# docker_process_sql and MARIADB_* env vars. Applies prisma/migrations/*/migration.sql
+# in order, so the container ends up schema-equivalent to a `prisma migrate deploy` run.
+for dir in /prisma-migrations/*/; do
+	file="${dir}migration.sql"
+	if [ -f "$file" ]; then
+		mysql_note "Applying Prisma migration: $file"
+		docker_process_sql --database="$MARIADB_DATABASE" < "$file"
+	fi
+done