fix: 统一数据库默认密码 change_me → cyrene_pass

Docker Compose 和 .env 使用 cyrene_pass，但 5 个 Go 源码文件
和 DevTools config.js 中的 fallback 密码仍是 change_me，
导致 memory-service/tool-engine/gateway 启动后 DB 认证失败。
修复 7 个文件中的硬编码 fallback 密码，统一为 cyrene_pass。

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docker-compose.dev.yml

@@ -7,7 +7,7 @@ services:
     image: pgvector/pgvector:pg16
     environment:
       POSTGRES_USER: cyrene
-      POSTGRES_PASSWORD: change_me
+      POSTGRES_PASSWORD: cyrene_pass
       POSTGRES_DB: cyrene_ai
     ports:
       - "5432:5432"
@@ -67,7 +67,7 @@ services:
       POSTGRES_HOST: postgres
       POSTGRES_PORT: "5432"
       POSTGRES_USER: cyrene
-      POSTGRES_PASSWORD: change_me
+      POSTGRES_PASSWORD: cyrene_pass
       POSTGRES_DB: cyrene_ai
     ports:
       - "8091:8091"
@@ -84,7 +84,7 @@ services:
       PORT: "8092"
       IOT_SERVICE_URL: http://iot-debug-service:8083
       DATA_DIR: /tmp/cyrene_data
-      DB_URL: "postgres://cyrene:change_me@postgres:5432/cyrene_ai?sslmode=disable"
+      DB_URL: "postgres://cyrene:cyrene_pass@postgres:5432/cyrene_ai?sslmode=disable"
     ports:
       - "8092:8092"
     depends_on:
@@ -119,7 +119,7 @@ services:
       POSTGRES_HOST: postgres
       POSTGRES_PORT: "5432"
       POSTGRES_USER: cyrene
-      POSTGRES_PASSWORD: change_me
+      POSTGRES_PASSWORD: cyrene_pass
       POSTGRES_DB: cyrene_ai
       IOT_DEBUG_SERVICE_URL: http://iot-debug-service:8083
       ENABLE_BACKGROUND_THINKING: ${ENABLE_BACKGROUND_THINKING:-true}
@@ -159,7 +159,7 @@ services:
       POSTGRES_HOST: postgres
       POSTGRES_PORT: "5432"
       POSTGRES_USER: cyrene
-      POSTGRES_PASSWORD: change_me
+      POSTGRES_PASSWORD: cyrene_pass
       POSTGRES_DB: cyrene_ai
       REDIS_HOST: redis
       REDIS_PORT: "6379"