Add Gitea entrypoint to generate app.ini from template on startup

Since app.ini is gitignored, the container needs to create it at
runtime. The entrypoint copies the template on first start, then
Gitea's env var overrides handle secrets.

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

docker-compose.yml

@@ -152,6 +152,7 @@ services:
     gitea:
         image: docker.gitea.com/gitea:1.25.4-rootless
         container_name: "${GITEA_HOST}"
+        entrypoint: ["/usr/bin/dumb-init", "--", "/etc/gitea/entrypoint.sh"]
         networks:
             - app-network
         environment:
@@ -169,6 +170,7 @@ services:
         volumes:
             - ./gitea/data:/var/lib/gitea
             - ./gitea/config:/etc/gitea
+            - ./gitea/entrypoint.sh:/etc/gitea/entrypoint.sh:ro
             - /etc/timezone:/etc/timezone:ro
             - /etc/localtime:/etc/localtime:ro
         ports: