feat(backend): implement database layer with models, schemas and repositories

Complete backend core implementation (BE-001 to BE-005):

BE-001: Database Connection & Session Management
- Create src/core/database.py with async SQLAlchemy 2.0
- Configure engine with pool_size=20
- Implement get_db() FastAPI dependency

BE-002: SQLAlchemy Models (5 models)
- Base model with TimestampMixin
- Scenario: status enum, relationships, cost tracking
- ScenarioLog: message hash, PII detection, metrics
- ScenarioMetric: time-series with extra_data (JSONB)
- AwsPricing: service pricing with region support
- Report: format enum, file tracking, extra_data

BE-003: Pydantic Schemas
- Scenario: Create, Update, Response, List schemas
- Log: Ingest, Response schemas
- Metric: Summary, CostBreakdown, MetricsResponse
- Common: PaginatedResponse generic type

BE-004: Base Repository Pattern
- Generic BaseRepository[T] with CRUD operations
- Methods: get, get_multi, count, create, update, delete
- Dynamic filter support

BE-005: Scenario Repository
- Extends BaseRepository[Scenario]
- Specific methods: get_by_name, list_by_status, list_by_region
- Business methods: update_status, increment_total_requests, update_total_cost
- ScenarioStatus enum
- Singleton instance: scenario_repository

All models, schemas and repositories tested and working.

Tasks: BE-001, BE-002, BE-003, BE-004, BE-005 complete

src/models/__init__.py

@@ -0,0 +1,17 @@
+"""Models package."""
+
+from src.models.base import Base
+from src.models.scenario import Scenario
+from src.models.scenario_log import ScenarioLog
+from src.models.scenario_metric import ScenarioMetric
+from src.models.aws_pricing import AwsPricing
+from src.models.report import Report
+
+__all__ = [
+    "Base",
+    "Scenario",
+    "ScenarioLog",
+    "ScenarioMetric",
+    "AwsPricing",
+    "Report",
+]

src/models/aws_pricing.py

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+"""AwsPricing model."""
+
+import uuid
+from sqlalchemy import Column, String, DECIMAL, Boolean, Date, Text
+from sqlalchemy.dialects.postgresql import UUID
+
+from src.models.base import Base
+
+
+class AwsPricing(Base):
+    """AWS service pricing model."""
+
+    __tablename__ = "aws_pricing"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    service = Column(String(50), nullable=False, index=True)
+    region = Column(String(50), nullable=False, index=True)
+    tier = Column(String(50), default="standard", nullable=False)
+    price_per_unit = Column(DECIMAL(15, 10), nullable=False)
+    unit = Column(String(20), nullable=False)
+    effective_from = Column(Date, nullable=False)
+    effective_to = Column(Date, nullable=True)
+    is_active = Column(Boolean, default=True, nullable=False)
+    source_url = Column(String(500), nullable=True)
+    description = Column(Text, nullable=True)

src/models/base.py

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+"""Base model with mixins."""
+
+from sqlalchemy import Column, DateTime
+from sqlalchemy.orm import declarative_base
+from sqlalchemy.sql import func
+
+Base = declarative_base()
+
+
+class TimestampMixin:
+    """Mixin che aggiunge created_at e updated_at."""
+
+    created_at = Column(
+        DateTime(timezone=True), server_default=func.now(), nullable=False
+    )
+    updated_at = Column(
+        DateTime(timezone=True),
+        server_default=func.now(),
+        onupdate=func.now(),
+        nullable=False,
+    )

src/models/report.py

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+"""Report model."""
+
+import uuid
+from sqlalchemy import Column, String, Integer, DateTime, ForeignKey, Enum
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+from sqlalchemy.orm import relationship
+
+from src.models.base import Base, TimestampMixin
+
+
+class Report(Base, TimestampMixin):
+    """Generated report tracking model."""
+
+    __tablename__ = "reports"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    scenario_id = Column(
+        UUID(as_uuid=True),
+        ForeignKey("scenarios.id", ondelete="CASCADE"),
+        nullable=False,
+    )
+    format = Column(Enum("pdf", "csv", name="report_format"), nullable=False)
+    file_path = Column(String(500), nullable=False)
+    file_size_bytes = Column(Integer, nullable=True)
+    generated_by = Column(String(100), nullable=True)
+    extra_data = Column(JSONB, default=dict)
+
+    # Relationships
+    scenario = relationship("Scenario", back_populates="reports")

src/models/scenario.py

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+"""Scenario model."""
+
+import uuid
+from sqlalchemy import Column, String, Text, Enum, DECIMAL, Integer, DateTime
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+from sqlalchemy.orm import relationship
+
+from src.models.base import Base, TimestampMixin
+
+
+class Scenario(Base, TimestampMixin):
+    """Scenario model for cost simulation."""
+
+    __tablename__ = "scenarios"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    name = Column(String(255), nullable=False)
+    description = Column(Text, nullable=True)
+    tags = Column(JSONB, default=list)
+    status = Column(
+        Enum("draft", "running", "completed", "archived", name="scenario_status"),
+        nullable=False,
+        default="draft",
+    )
+    region = Column(String(50), nullable=False, default="us-east-1")
+    completed_at = Column(DateTime(timezone=True), nullable=True)
+    started_at = Column(DateTime(timezone=True), nullable=True)
+    total_requests = Column(Integer, default=0, nullable=False)
+    total_cost_estimate = Column(DECIMAL(12, 6), default=0.0, nullable=False)
+
+    # Relationships
+    logs = relationship(
+        "ScenarioLog", back_populates="scenario", cascade="all, delete-orphan"
+    )
+    metrics = relationship(
+        "ScenarioMetric", back_populates="scenario", cascade="all, delete-orphan"
+    )
+    reports = relationship(
+        "Report", back_populates="scenario", cascade="all, delete-orphan"
+    )

src/models/scenario_log.py

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+"""ScenarioLog model."""
+
+import uuid
+from sqlalchemy import Column, String, Integer, Boolean, DateTime, ForeignKey
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import relationship
+
+from src.models.base import Base
+
+
+class ScenarioLog(Base):
+    """Log entry model for received logs."""
+
+    __tablename__ = "scenario_logs"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    scenario_id = Column(
+        UUID(as_uuid=True),
+        ForeignKey("scenarios.id", ondelete="CASCADE"),
+        nullable=False,
+    )
+    received_at = Column(DateTime(timezone=True), nullable=False)
+    message_hash = Column(String(64), nullable=False, index=True)
+    message_preview = Column(String(500), nullable=True)
+    source = Column(String(100), default="unknown", nullable=False)
+    size_bytes = Column(Integer, default=0, nullable=False)
+    has_pii = Column(Boolean, default=False, nullable=False)
+    token_count = Column(Integer, default=0, nullable=False)
+    sqs_blocks = Column(Integer, default=1, nullable=False)
+
+    # Relationships
+    scenario = relationship("Scenario", back_populates="logs")

src/models/scenario_metric.py

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+"""ScenarioMetric model."""
+
+import uuid
+from sqlalchemy import Column, String, DECIMAL, DateTime, ForeignKey
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+from sqlalchemy.orm import relationship
+
+from src.models.base import Base
+
+
+class ScenarioMetric(Base):
+    """Metric time-series model for scenario analytics."""
+
+    __tablename__ = "scenario_metrics"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    scenario_id = Column(
+        UUID(as_uuid=True),
+        ForeignKey("scenarios.id", ondelete="CASCADE"),
+        nullable=False,
+    )
+    timestamp = Column(DateTime(timezone=True), nullable=False)
+    metric_type = Column(
+        String(50), nullable=False
+    )  # 'sqs', 'lambda', 'bedrock', 'safety'
+    metric_name = Column(String(100), nullable=False)
+    value = Column(DECIMAL(15, 6), default=0.0, nullable=False)
+    unit = Column(String(20), nullable=False)  # 'count', 'bytes', 'tokens', 'usd'
+    extra_data = Column(JSONB, default=dict)
+
+    # Relationships
+    scenario = relationship("Scenario", back_populates="metrics")