feat: add DB service block to docker-compose-gitea template

Add DB_SERVICE_START/END markers for the database container and
DB_DEPENDS_START/END for the gitea service depends_on. Phase scripts
strip these blocks for sqlite3 and populate DB-specific vars
(image, env, healthcheck, data dir) for mysql/postgres/mssql.

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

templates/docker-compose-gitea.yml.tpl

@@ -1,14 +1,36 @@
 # Gitea Docker Compose — rendered by phase1_gitea_unraid.sh and phase2_gitea_fedora.sh
 # Variables: GITEA_VERSION, DATA_PATH, GITEA_PORT, GITEA_SSH_PORT
 # DATA_PATH is host-specific (UNRAID_GITEA_DATA_PATH or FEDORA_GITEA_DATA_PATH)
+# DB_SERVICE block is stripped for sqlite3, kept for mysql/postgres/mssql.
 
 version: "3"
 
 services:
+# DB_SERVICE_START
+  db:
+    image: ${DB_DOCKER_IMAGE}
+    container_name: gitea-db
+    restart: unless-stopped
+    environment:
+${DB_ENV_VARS}
+    volumes:
+      - ${DATA_PATH}/db:/var/lib/${DB_DATA_DIR}
+    healthcheck:
+      test: ${DB_HEALTHCHECK}
+      interval: 10s
+      timeout: 5s
+      retries: 5
+# DB_SERVICE_END
+
   gitea:
     image: gitea/gitea:${GITEA_VERSION}
     container_name: gitea
     restart: unless-stopped
+# DB_DEPENDS_START
+    depends_on:
+      db:
+        condition: service_healthy
+# DB_DEPENDS_END
     environment:
       - USER_UID=1000
       - USER_GID=1000