feat: database models and alembic migrations — all tables per design

- shared/db.py: async engine + session factory
- shared/models/base.py: DeclarativeBase + TimestampMixin
- shared/models/trading.py: Strategy, Signal, Trade, Position, StrategyWeightHistory
- shared/models/news.py: Article, ArticleSentiment
- shared/models/learning.py: TradeOutcome, LearningAdjustment
- shared/models/auth.py: User, UserCredential
- shared/models/timeseries.py: MarketData, PortfolioSnapshot, StrategyMetric
- Alembic async env.py with initial migration including TimescaleDB hypertables
- 21 model tests covering enums, instantiation, metadata registration

shared/models/learning.py

@@ -0,0 +1,51 @@
+"""Learning domain models: TradeOutcome, LearningAdjustment."""
+
+import uuid
+from datetime import timedelta
+
+from sqlalchemy import Boolean, Float, ForeignKey, Interval, String, Text
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from shared.models.base import Base, TimestampMixin
+
+
+class TradeOutcome(TimestampMixin, Base):
+    __tablename__ = "trade_outcomes"
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), primary_key=True, default=uuid.uuid4
+    )
+    trade_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("trades.id"), unique=True, nullable=False
+    )
+    hold_duration: Mapped[timedelta | None] = mapped_column(Interval, nullable=True)
+    realized_pnl: Mapped[float] = mapped_column(Float, nullable=False)
+    roi_pct: Mapped[float] = mapped_column(Float, nullable=False)
+    was_profitable: Mapped[bool] = mapped_column(Boolean, nullable=False)
+
+    # Relationships
+    trade: Mapped["Trade"] = relationship("Trade", back_populates="outcome")
+
+
+class LearningAdjustment(TimestampMixin, Base):
+    __tablename__ = "learning_adjustments"
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), primary_key=True, default=uuid.uuid4
+    )
+    strategy_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("strategies.id"), nullable=False
+    )
+    old_weight: Mapped[float] = mapped_column(Float, nullable=False)
+    new_weight: Mapped[float] = mapped_column(Float, nullable=False)
+    reason: Mapped[str | None] = mapped_column(Text, nullable=True)
+    reward_signal: Mapped[float] = mapped_column(Float, nullable=False)
+
+    # Relationships
+    strategy: Mapped["Strategy"] = relationship("Strategy")
+
+
+# Avoid circular imports — reference by string in relationship()
+from shared.models.trading import Trade as Trade  # noqa: E402, F401
+from shared.models.trading import Strategy as Strategy  # noqa: E402, F401