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/__init__.py

@@ -1,14 +1,11 @@
 """Database models and shared metadata for the CalMiner domain."""
 
-from .financial_input import FinancialCategory, FinancialInput
+from .financial_input import FinancialInput
 from .metadata import (
     COST_BUCKET_METADATA,
     RESOURCE_METADATA,
     STOCHASTIC_VARIABLE_METADATA,
-    CostBucket,
     ResourceDescriptor,
-    ResourceType,
-    StochasticVariable,
     StochasticVariableDescriptor,
 )
 from .performance_metric import PerformanceMetric
@@ -17,9 +14,18 @@ from .pricing_settings import (
     PricingMetalSettings,
     PricingSettings,
 )
-from .project import MiningOperationType, Project
-from .scenario import Scenario, ScenarioStatus
-from .simulation_parameter import DistributionType, SimulationParameter
+from .enums import (
+    CostBucket,
+    DistributionType,
+    FinancialCategory,
+    MiningOperationType,
+    ResourceType,
+    ScenarioStatus,
+    StochasticVariable,
+)
+from .project import Project
+from .scenario import Scenario
+from .simulation_parameter import SimulationParameter
 from .user import Role, User, UserRole, password_context
 
 __all__ = [