compose: healthcheck on ingest, stream waits for it

Add a Docker healthcheck probing ingest's /healthz (via python, since the slim
image has neither curl nor wget) and make the stream start only once ingest is
service_healthy, so it never briefly falls back on an empty cache at boot.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docker-compose.yml

@@ -29,13 +29,22 @@ services:
       # Canonicalizer MusicBrainz (identité MBID inter-sources ; sans clé).
       - RADIEO_CANONICAL_ENABLED=${RADIEO_CANONICAL_ENABLED:-1}
       - RADIEO_USER_AGENT=${RADIEO_USER_AGENT:-radieo/0.1 (personal music radio)}
+    healthcheck:
+      # python-slim n'a ni curl ni wget : on sonde /healthz en Python.
+      test: ["CMD", "python", "-c",
+             "import urllib.request; urllib.request.urlopen('http://localhost:8080/healthz')"]
+      interval: 30s
+      timeout: 5s
+      retries: 3
+      start_period: 10s
     restart: unless-stopped
 
   stream:
     build: ./stream
     image: radieo-stream
     depends_on:
-      - ingest
+      ingest:
+        condition: service_healthy
     ports:
       - "8000:8000"             # flux HTTP : http://localhost:8000/radio.mp3
     volumes: