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/manual.yaml

@@ -0,0 +1,20 @@
+kind: manual
+label: 固定 / 可变费率（NL，双费率）
+
+energy:
+  dual_tariff: true              # use delivered_1/2, returned_1/2 for low/high tariffs
+  buy:
+    normal: { unit: EUR/kWh }   # high-tariff buy price (delivered_2 register)
+    dal:    { unit: EUR/kWh }   # low-tariff buy price (delivered_1 register)
+  sell:
+    normal: { unit: EUR/kWh }   # high-tariff sell / return price
+    dal:    { unit: EUR/kWh }   # low-tariff sell / return price (currently equal to normal)
+  energy_tax: { unit: EUR/kWh } # energy tax added to buy price (incl. VAT)
+  ode:        { unit: EUR/kWh, default: 0 }  # currently merged into energy_tax
+
+standing:                        # fixed charges; UI fills per month, engine prorates to days
+  network_fee:    { unit: EUR/month }
+  management_fee: { unit: EUR/month }
+
+credits:
+  heffingskorting: { unit: EUR/year }  # energy-tax credit; deducted at summary layer