Refactor database initialization and remove Alembic migrations

- Removed legacy Alembic migration files and consolidated schema management into a new Pydantic-backed initializer (`scripts/init_db.py`).
- Updated `main.py` to ensure the new DB initializer runs on startup, maintaining idempotency.
- Adjusted session management in `config/database.py` to prevent DetachedInstanceError.
- Introduced new enums in `models/enums.py` for better organization and clarity.
- Refactored various models to utilize the new enums, improving code maintainability.
- Enhanced middleware to handle JSON validation more robustly, ensuring non-JSON requests do not trigger JSON errors.
- Added tests for middleware and enums to ensure expected behavior and consistency.
- Updated changelog to reflect significant changes and improvements.

models/financial_input.py

@@ -1,7 +1,6 @@
 from __future__ import annotations
 
 from datetime import date, datetime
-from enum import Enum
 from typing import TYPE_CHECKING
 
 from sqlalchemy import (
@@ -19,23 +18,13 @@ from sqlalchemy.orm import Mapped, mapped_column, relationship, validates
 from sqlalchemy.sql import func
 
 from config.database import Base
-from .metadata import CostBucket
+from .enums import CostBucket, FinancialCategory
 from services.currency import normalise_currency
 
 if TYPE_CHECKING:  # pragma: no cover
     from .scenario import Scenario
 
 
-class FinancialCategory(str, Enum):
-    """Enumeration of cost and revenue classifications."""
-
-    CAPITAL_EXPENDITURE = "capex"
-    OPERATING_EXPENDITURE = "opex"
-    REVENUE = "revenue"
-    CONTINGENCY = "contingency"
-    OTHER = "other"
-
-
 class FinancialInput(Base):
     """Line-item financial assumption attached to a scenario."""
 
@@ -47,10 +36,10 @@ class FinancialInput(Base):
     )
     name: Mapped[str] = mapped_column(String(255), nullable=False)
     category: Mapped[FinancialCategory] = mapped_column(
-        SQLEnum(FinancialCategory), nullable=False
+        SQLEnum(FinancialCategory, name="financialcategory", create_type=False), nullable=False
     )
     cost_bucket: Mapped[CostBucket | None] = mapped_column(
-        SQLEnum(CostBucket), nullable=True
+        SQLEnum(CostBucket, name="costbucket", create_type=False), nullable=True
     )
     amount: Mapped[float] = mapped_column(Numeric(18, 2), nullable=False)
     currency: Mapped[str | None] = mapped_column(String(3), nullable=True)