feat(backend): каркас — конфиг, движок БД, базовые модели и первая миграция

SQLAlchemy 2 async на asyncpg, Alembic, pydantic-settings. Деньги везде
NUMERIC(24,10) с колонкой валюты рядом (db/base.py), postgres-enum'ы хранят
значения, а не имена, чтобы база читалась так же, как API.

Первая миграция: app_user, account, portfolio, instrument, sync_run, sync_job.
metrics/refresh.py задаёт порядок пересборки metric_* и сериализует параллельные
пересчёты advisory-локом на отдельном соединении: каждый шаг заменяет свою
таблицу целиком, два одновременных прогона затёрли бы друг друга.

backend/src/fintracker/models/__init__.py

@@ -0,0 +1,136 @@
+"""ORM models. Importing this package registers every table on `Base.metadata`."""
+
+from fintracker.models.accounts import (
+    Account,
+    AccountKind,
+    AccountLink,
+    AccountRole,
+    Broker,
+    EventSource,
+    Portfolio,
+    PortfolioAccount,
+)
+from fintracker.models.auth import AppUser, RefreshToken
+from fintracker.models.instruments import AssetClass, Instrument, InstrumentAlias
+from fintracker.models.ledger import (
+    EXTERNAL_FLOW_KINDS,
+    POSITION_KINDS,
+    Event,
+    EventKind,
+    EventStatus,
+    Lot,
+    LotDisposal,
+)
+from fintracker.models.metrics import (
+    MetricCashFlowMonthly,
+    MetricDataQuality,
+    MetricHolding,
+    MetricNetWorthDaily,
+    MetricPortfolioValueDaily,
+    MetricRefreshLog,
+    MetricReturns,
+    MetricRunway,
+    MetricSpendingByCategory,
+)
+from fintracker.models.pricing import (
+    CashSnapshot,
+    CorporateAction,
+    CorporateActionKind,
+    CorporateActionStatus,
+    FxRateDaily,
+    PositionSnapshot,
+    PriceDaily,
+    PriceLast,
+    PriceManual,
+    RawCbrRate,
+)
+from fintracker.models.sync import (
+    JobStatus,
+    RunStatus,
+    SourceCredential,
+    SyncJob,
+    SyncRun,
+    SyncState,
+)
+from fintracker.models.tinvest import (
+    RawTinvestEvent,
+    RawTinvestInstrument,
+    RawTinvestOperation,
+    RawTinvestSnapshot,
+)
+from fintracker.models.zenmoney import (
+    CashTxn,
+    CashTxnTag,
+    Category,
+    FlowType,
+    Merchant,
+    RawZenmoneyDeletion,
+    RawZenmoneyEntity,
+    Rule,
+    RuleKind,
+    RuleMatchType,
+    Trip,
+)
+
+__all__ = [
+    "EXTERNAL_FLOW_KINDS",
+    "POSITION_KINDS",
+    "Account",
+    "AccountKind",
+    "AccountLink",
+    "AccountRole",
+    "AppUser",
+    "AssetClass",
+    "Broker",
+    "CashSnapshot",
+    "CashTxn",
+    "CashTxnTag",
+    "Category",
+    "CorporateAction",
+    "CorporateActionKind",
+    "CorporateActionStatus",
+    "Event",
+    "EventKind",
+    "EventSource",
+    "EventStatus",
+    "FlowType",
+    "FxRateDaily",
+    "Instrument",
+    "InstrumentAlias",
+    "JobStatus",
+    "Lot",
+    "LotDisposal",
+    "Merchant",
+    "MetricCashFlowMonthly",
+    "MetricDataQuality",
+    "MetricHolding",
+    "MetricNetWorthDaily",
+    "MetricPortfolioValueDaily",
+    "MetricRefreshLog",
+    "MetricReturns",
+    "MetricRunway",
+    "MetricSpendingByCategory",
+    "Portfolio",
+    "PortfolioAccount",
+    "PositionSnapshot",
+    "PriceDaily",
+    "PriceLast",
+    "PriceManual",
+    "RawCbrRate",
+    "RawTinvestEvent",
+    "RawTinvestInstrument",
+    "RawTinvestOperation",
+    "RawTinvestSnapshot",
+    "RawZenmoneyDeletion",
+    "RawZenmoneyEntity",
+    "RefreshToken",
+    "Rule",
+    "RuleKind",
+    "RuleMatchType",
+    "RunStatus",
+    "SourceCredential",
+    "SyncJob",
+    "SyncRun",
+    "SyncState",
+    "Trip",
+]