refactor: replace universal_migration.py with Alembic

Remove the 7,791-line universal_migration.py and 16 incomplete individual
Alembic migrations. Replace with a single initial schema migration using
Base.metadata.create_all(checkfirst=True).

Changes:
- Add programmatic Alembic runner (app/database/migrations.py) with
  auto-stamp logic for existing databases transitioning from
  universal_migration
- Extract ensure_default_web_api_token() to web_api_token_service.py
- Extract sync_postgres_sequences() to database.py with SQL injection
  prevention via _quote_ident()
- Add HMAC token hashing support with backward-compatible dual-hash
  fallback and automatic rehashing
- Remove dead init_db() function and unused imports
- Add Makefile targets: migrate, migration, migrate-stamp, migrate-history
- Fix fileConfig() destroying structlog config (disable_existing_loggers)
- Remove duplicate migrations/alembic/alembic.ini with credentials
- Add script.py.mako template for future migration generation
- Update startup flow: alembic upgrade → sync sequences → ensure token
- Harden database.py: ParamSpec for retry decorator, safe URL logging,
  echo='debug' mode, execute_with_retry validation
- Update documentation references

31 files changed, 302 insertions(+), 9,226 deletions(-)

docs/project_structure_reference.md

@@ -62,9 +62,9 @@
 - `app/database/models.py` — Python-модуль
   Классы: `UserStatus`, `SubscriptionStatus`, `TransactionType`, `PromoCodeType`, `PaymentMethod`, `MainMenuButtonActionType`, `MainMenuButtonVisibility`, `YooKassaPayment` (6 методов), `CryptoBotPayment` (5 методов), `MulenPayPayment` (2 методов), `Pal24Payment` (3 методов), `PromoGroup` (3 методов), `User` (5 методов), `Subscription` (11 методов), `Transaction` (1 методов), `SubscriptionConversion` (2 методов), `PromoCode` (2 методов), `PromoCodeUse`, `ReferralEarning` (1 методов), `Squad` (1 методов), `ServiceRule`, `PrivacyPolicy`, `PublicOffer`, `FaqSetting`, `FaqPage`, `SystemSetting`, `MonitoringLog`, `SentNotification`, `DiscountOffer`, `PromoOfferTemplate`, `SubscriptionTemporaryAccess`, `PromoOfferLog`, `BroadcastHistory`, `ServerSquad` (3 методов), `SubscriptionServer`, `SupportAuditLog`, `UserMessage` (1 методов), `WelcomeText`, `AdvertisingCampaign` (2 методов), `AdvertisingCampaignRegistration` (1 методов), `TicketStatus`, `Ticket` (8 методов), `TicketMessage` (3 методов), `WebApiToken` (1 методов), `MainMenuButton` (3 методов)
   Функции: нет
-- `app/database/universal_migration.py` — Python-модуль
+- `app/database/migrations.py` — Programmatic Alembic migration runner
   Классы: нет
-  Функции: нет
+  Функции: `run_alembic_upgrade`, `stamp_alembic_head`
 
 #### app/database/crud