refactor(pricing): make the service the only price source

Price lists, annual tariffs and per-branch price overrides each answered
"what does this service cost?" differently, so a single date could carry
several answers and nobody could say which one was right. Price now lives
only on ServiceItem.price_rials, edited from the services page.

- drop PriceList/PriceListItem, their repositories and the seven
  /api/v1/price-list(s) endpoints; PricingController keeps only quote and
  the appointment price snapshot
- drop Tariff, TariffRepository, TariffService and the two
  /service-items/{uuid}/tariffs endpoints; creating or repricing a service
  no longer upserts a current-year tariff
- drop price_rials from ServiceBranchOverride; the entity stays for its
  duration columns, which DurationCalculator and ServiceSelectionValidator
  still read
- InvoiceService reads the item price directly
- PricingEngine collapses to a single source; breakdown.sources always
  reports service_item, keeping the response contract intact
- remove the price-lists admin page, its route and settings-menu entry, the
  tariff modal and the service detail tariffs tab; useAppointmentInvoice
  moves to its own hook file

Migration drops price_lists, price_list_items, service_tariffs and the
override price column.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/api/billing.md

@@ -8,7 +8,7 @@
 
 صورتحساب (`Invoice`) از یک Encounter (`PatientSession`) ساخته می‌شود. برای هر آیتم سهم بیمه‌ی پایه، بیمه‌ی مکمل و بیمار با `BillingCalculator` محاسبه می‌شود:
 
-- تعرفه‌ی خدمت از `Tariff` سال جاری (با fallback به `ServiceItem.priceRials`).
+- قیمت خدمت از `ServiceItem.priceRials` — تنها منبع قیمت.
 - قانون پوشش از قرارداد بیمه‌ی tenant (`TenantInsurance`) + override خدمت (`TenantServiceCoverage`).
 - درصد پوشش به تفکیک **نوع خدمت** و از زنجیرهٔ resolve توضیح‌داده‌شده در [insurance.md](insurance.md#قاعدهٔ-درصد-پوشش-coverage-percent-model) گرفته می‌شود: هر خدمت با `ServiceItem.service_category` خودش، و **ویزیت** با `PatientSession.insurance_service_category` (نوعی که سرِ پذیرش انتخاب شده؛ در نبودش سرپایی).
 - `invoices.service_category` همان نوع را snapshot می‌کند و در `toArray()` به‌صورت `service_category` / `service_category_label` برمی‌گردد.