feat(deploy): healthcheck on /health, compose uses GHCR image

railway.toml: point Railway's healthcheck at /health. Fabro's server
returns 200 for any unknown path (SPA fallback) so /healthz would have
been a false-positive check that never catches failures. /health is
the real endpoint exposed by fabro-server and documented in the
OpenAPI spec.

docker-compose.yaml: swap `build: Dockerfile` for
`image: ghcr.io/fabro-sh/fabro:nightly`. A fresh clone's `docker
compose up` previously failed because the Dockerfile expects pre-built
binaries under `docker-context/` that only the release workflow
populates. Pulling the published image gives new users a 5-second
boot and mirrors the Railway deployment shape. Pin to linux/amd64
until the arm64 image variant is fixed.

docker-compose.yaml

@@ -1,9 +1,7 @@
 services:
   fabro:
-    image: fabro
-    build:
-      context: .
-      dockerfile: Dockerfile
+    image: ghcr.io/fabro-sh/fabro:nightly
+    platform: linux/amd64
     ports:
       - "32276:32276"
     volumes:

railway.toml

@@ -3,5 +3,6 @@ builder = "dockerfile"
 dockerfilePath = "Dockerfile.deploy"
 
 [deploy]
+healthcheckPath = "/health"
 restartPolicyType = "on_failure"
 restartPolicyMaxRetries = 5