M6-T03: add pricing profile framework + strategy registry

- app/integrations/pricing: profiles.py (pydantic ManualProfile/TibberProfile,
  load_profile/list_profiles/validate_values), manual.yaml + tibber.yaml
  (structure-only, no price values), strategies.py (register/get_strategy,
  manual dual-tariff + tibber strategies, all Decimal).
- tibber strategy matches nearest tibber_price with starts_at <= t0.
- tests for profiles + strategies (hand-checked dual-tariff & tibber math).

app/integrations/pricing/profiles/tibber.yaml

@@ -0,0 +1,14 @@
+kind: tibber
+label: Tibber 动态电价（15 分钟）
+
+energy:
+  source: tibber_api              # buy = total (from API); sell = total − energy_tax − sell_adjust
+  energy_tax:  { unit: EUR/kWh }  # subtracted from total to derive sell price (incl. VAT)
+  sell_adjust: { unit: EUR/kWh, default: 0 }  # additional sell-price adjustment (residual spread)
+
+standing:                         # fixed charges; UI fills per month, engine prorates to days
+  management_fee: { unit: EUR/month, default: 5.99 }
+  network_fee:    { unit: EUR/month }
+
+credits:
+  heffingskorting: { unit: EUR/year }  # energy-tax credit; deducted at summary layer