fix: mount custom sign-in UI over Logto experience dist

CUSTOM_UI_PATH is a Logto Cloud feature, not available in OSS.
The correct approach for self-hosted Logto is to volume-mount
over /etc/logto/packages/experience/dist/.

- Use init container (sign-in-ui) to copy dist to shared volume
  as root (fixes permission denied with cameleer user)
- Logto mounts signinui volume at experience/dist path
- Logto depends on sign-in-ui init container completion
- Remove saas-entrypoint.sh approach (no longer needed)
- Revert Dockerfile entrypoint to direct java -jar
- Permit /favicon.svg in SecurityConfig for sign-in page logo

Tested: full OIDC flow works end-to-end via Playwright.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -63,15 +63,16 @@ services:
     depends_on:
       postgres:
         condition: service_healthy
+      sign-in-ui:
+        condition: service_completed_successfully
     entrypoint: ["sh", "-c", "npm run cli db seed -- --swe && npm start"]
     volumes:
-      - signinui:/etc/logto/custom-ui
+      - signinui:/etc/logto/packages/experience/dist
     environment:
       DB_URL: postgres://${POSTGRES_USER:-cameleer}:${POSTGRES_PASSWORD:-cameleer_dev}@postgres:5432/logto
       ENDPOINT: ${PUBLIC_PROTOCOL:-https}://${PUBLIC_HOST:-localhost}
       ADMIN_ENDPOINT: http://${PUBLIC_HOST:-localhost}:3002
       TRUST_PROXY_HEADER: 1
-      CUSTOM_UI_PATH: /etc/logto/custom-ui
     healthcheck:
       test: ["CMD-SHELL", "node -e \"require('http').get('http://localhost:3001/oidc/.well-known/openid-configuration', r => process.exit(r.statusCode === 200 ? 0 : 1)).on('error', () => process.exit(1))\""]
       interval: 5s
@@ -121,6 +122,14 @@ services:
     networks:
       - cameleer
 
+  sign-in-ui:
+    image: ${CAMELEER_IMAGE:-gitea.siegeln.net/cameleer/cameleer-saas}:${VERSION:-latest}
+    restart: "no"
+    user: root
+    entrypoint: ["sh", "-c", "cp -r /app/sign-in-dist/* /data/sign-in-ui/ && echo '[sign-in-ui] Copied custom UI to shared volume'"]
+    volumes:
+      - signinui:/data/sign-in-ui
+
   cameleer-saas:
     image: ${CAMELEER_IMAGE:-gitea.siegeln.net/cameleer/cameleer-saas}:${VERSION:-latest}
     restart: unless-stopped
@@ -133,7 +142,6 @@ services:
       - /var/run/docker.sock:/var/run/docker.sock
       - jardata:/data/jars
       - bootstrapdata:/data/bootstrap:ro
-      - signinui:/data/sign-in-ui
     environment:
       SPRING_DATASOURCE_URL: jdbc:postgresql://postgres:5432/${POSTGRES_DB:-cameleer_saas}
       SPRING_DATASOURCE_USERNAME: ${POSTGRES_USER:-cameleer}