M6-T05: add Tibber GraphQL client + price refresh service + schedule

- app/integrations/tibber/client.py: fetch_price_range/fetch_current_price
  (priceInfoRange QUARTER_HOURLY, startsAt->UTC, no fixed node count assumption),
  TibberError/TibberAuthError; token never logged or put in exception text.
- app/services/tibber_prices.py: refresh_prices upserts by starts_at (idempotent),
  no-op unless an active kind=tibber contract + token exist.
- main.py: hourly tibber-refresh job (existing jobs/MQTT untouched). Tests added.

docs/design/m6-tibber-dynamic-energy.md

@@ -347,7 +347,7 @@ Phase D（API + 前端）
 - **Reviewer checklist**: 版本只增不改（不覆盖旧版本）；激活互斥；删除受 FK RESTRICT（有版本/有费用记录不可裸删）；数值校验走 T03 `validate_values`；路径键用合同 id。
 
 ### M6-T05 — Tibber 客户端 + 抓价 service + 调度 + tibber/test
-- **Status**: `todo` · **Depends**: M6-T01, M6-T02, M6-T03
+- **Status**: `done` · **Depends**: M6-T01, M6-T02, M6-T03
 - **Context**: httpx 拉 15min 价 upsert `tibber_price`；启动+每日抓（仅 active=tibber）；连接测试。
 - **Files**: `create app/integrations/tibber/__init__.py`、`tibber/client.py`、`app/services/tibber_prices.py`；`modify app/main.py`（抓价 job）；`create tests/test_tibber_client.py`、`tests/test_tibber_prices.py`
 - **Steps**: