T17: backend penyimpanan bersama db.py (sqlite | mysql via PyMySQL)

- db.py: abstraksi connect/query/queryone/replace_snapshot; %s → ? utk sqlite;
  replace snapshot mysql = CREATE IF NOT EXISTS + DELETE + INSERT (MVCC)
- config/.env.example: VEX_DB_BACKEND (default sqlite) + VEX_DB_HOST/PORT/USER/PASS/NAME
- get_voters.persist → db.replace_snapshot; dashboard baca via db.query
- LIKE pakai ESCAPE '!' (backslash memutus literal string MySQL, B2);
  db.query selalu kembalikan list (PyMySQL tuple vs sqlite list, B3)
- docker-compose.yml: kontainer uji mariadb:11 (databisnisid-mariadb, 127.0.0.1:3306)
- test_mariadb.py: suite integrasi opt-in (skip bila bukan mysql)
- SPEC.md §V17/T17/B2/B3; AGENTS.md runbook

docker-compose.yml

@@ -0,0 +1,22 @@
+services:
+  mariadb:
+    image: mariadb:11
+    container_name: databisnisid-mariadb
+    restart: unless-stopped
+    environment:
+      MARIADB_ROOT_PASSWORD: ${MARIADB_ROOT_PASSWORD:-root}
+      MARIADB_DATABASE: ${MARIADB_DATABASE:-databisnisid}
+      MARIADB_USER: ${MARIADB_USER:-databisnis}
+      MARIADB_PASSWORD: ${MARIADB_PASSWORD:-databisnis}
+    ports:
+      - "127.0.0.1:3306:3306"
+    volumes:
+      - mariadb_data:/var/lib/mysql
+    healthcheck:
+      test: ["CMD", "healthcheck.sh", "--connect", "--innodb_initialized"]
+      interval: 5s
+      timeout: 5s
+      retries: 12
+
+volumes:
+  mariadb_data: