fix: delete agent 500 error + dynamic personality + deployment guide

- Fix delete agent 500: clean up FK records (agent_llm_logs, permissions,
  schedules, executions, team_members) and unbind goals/tasks before delete
- Remove hardcoded personality templates in Android, replace with dynamic
  system prompt generation from name + description
- Set promptSectionsEnabled=false to bypass PromptComposer for personality
- Add Tencent Cloud Linux deployment guide (Docker Compose)
- Accumulated backend service updates, frontend UI fixes, Android app changes

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

backend/.env.example

@@ -7,6 +7,8 @@
 # 应用
 APP_NAME=天工智能体平台
 APP_VERSION=1.0.0
+# 运行环境: dev (开发) | staging (预发布) | prod (生产)
+ENVIRONMENT=dev
 DEBUG=False
 
 # 安全密钥（生产环境务必修改！）
@@ -27,6 +29,11 @@ CORS_ORIGINS=http://localhost:8038,http://localhost:3000
 # 外部访问地址（用于通知中的链接）
 EXTERNAL_URL=http://localhost:8037
 
+# HSTS 安全头（生产环境建议启用）
+HSTS_ENABLED=False
+HSTS_MAX_AGE=31536000
+HSTS_INCLUDE_SUBDOMAINS=True
+
 # ─── AI 模型 API Key ⚠️ 敏感信息 ───
 # 至少配置一个
 OPENAI_API_KEY=
@@ -37,6 +44,11 @@ ANTHROPIC_API_KEY=
 SILICONFLOW_API_KEY=
 SILICONFLOW_BASE_URL=https://api.siliconflow.cn/v1
 
+# 全局 LLM 降级配置（当 Agent 未单独配置 fallback 时自动启用）
+FALLBACK_LLM_MODEL=
+FALLBACK_LLM_API_KEY=
+FALLBACK_LLM_BASE_URL=
+
 # ─── 飞书应用（可选） ───
 FEISHU_APP_ID=
 FEISHU_APP_SECRET=