fix: rename sidecar() helper → callSidecar() and fix mariadb healthcheck

The new `const sidecar` axios instance (added in 243e5d3) clashed with the
pre-existing `async function sidecar()` fetch helper, causing `npm run build`
to fail with a rolldown redeclaration error. Rename the fetch helper and all
its call sites to `callSidecar`.

Also replace the mariadb healthcheck command: `healthcheck.sh` calls the
`mariadb` CLI which isn't on PATH in the current image layer, causing the
container to stay permanently unhealthy and the deploy webhook to abort before
the `npm run build` step runs — leaving the old JS bundle serving from nginx.
Switch to `mysqladmin ping` which is available in all MariaDB 11 images.

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

docker-compose.yml

@@ -42,7 +42,7 @@ services:
       # silently no-op on Debian/Ubuntu and macOS Docker Desktop.
       - ./mariadb/init:/docker-entrypoint-initdb.d:ro,Z
     healthcheck:
-      test: ["CMD", "healthcheck.sh", "--connect", "--innodb_initialized"]
+      test: ["CMD", "mysqladmin", "ping", "-h", "127.0.0.1", "--silent"]
       interval: 10s
       timeout: 5s
       retries: 12