feat(ai): AI 健康管家 V2 基础设施 — 功能开关 + 角色沙箱准备 + 体征页 AI 趋势分析

- 迁移 000153: 新增 ai_feature_flags / ai_usage_daily / ai_suggestion_feedback 三张表,
  ai_tenant_configs 增加 billing_enabled 列, seed 12 个功能开关 + 2 个管理权限码
- 新增 FeatureFlagService: 5 分钟缓存 + DB 回退 + 即时更新
- VitalSignsTab 添加 AI 趋势分析按钮 (SSE 流式)
- 新增 3 个 Entity (ai_feature_flags / ai_usage_daily / ai_suggestion_feedback)
- AiState 扩展 feature_flags 字段
- 设计规格 + 讨论记录文档

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

crates/erp-ai/src/state.rs

@@ -7,6 +7,7 @@ use sea_orm::DatabaseConnection;
 use crate::provider::registry::ProviderRegistry;
 use crate::service::analysis::AnalysisService;
 use crate::service::cache::CacheService;
+use crate::service::feature_flag_service::FeatureFlagService;
 use crate::service::insight_service::InsightService;
 use crate::service::prompt::PromptService;
 use crate::service::quota::QuotaService;
@@ -28,4 +29,5 @@ pub struct AiState {
     pub cache: Arc<CacheService>,
     pub risk_service: Arc<RiskService>,
     pub insight_service: Arc<InsightService>,
+    pub feature_flags: Arc<FeatureFlagService>,
 }