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/metadata.py

@@ -1,45 +1,7 @@
 from __future__ import annotations
 
 from dataclasses import dataclass
-from enum import Enum
-
-
-class ResourceType(str, Enum):
-    """Primary consumables and resources used in mining operations."""
-
-    DIESEL = "diesel"
-    ELECTRICITY = "electricity"
-    WATER = "water"
-    EXPLOSIVES = "explosives"
-    REAGENTS = "reagents"
-    LABOR = "labor"
-    EQUIPMENT_HOURS = "equipment_hours"
-    TAILINGS_CAPACITY = "tailings_capacity"
-
-
-class CostBucket(str, Enum):
-    """Granular cost buckets aligned with project accounting."""
-
-    CAPITAL_INITIAL = "capital_initial"
-    CAPITAL_SUSTAINING = "capital_sustaining"
-    OPERATING_FIXED = "operating_fixed"
-    OPERATING_VARIABLE = "operating_variable"
-    MAINTENANCE = "maintenance"
-    RECLAMATION = "reclamation"
-    ROYALTIES = "royalties"
-    GENERAL_ADMIN = "general_admin"
-
-
-class StochasticVariable(str, Enum):
-    """Domain variables that typically require probabilistic modelling."""
-
-    ORE_GRADE = "ore_grade"
-    RECOVERY_RATE = "recovery_rate"
-    METAL_PRICE = "metal_price"
-    OPERATING_COST = "operating_cost"
-    CAPITAL_COST = "capital_cost"
-    DISCOUNT_RATE = "discount_rate"
-    THROUGHPUT = "throughput"
+from .enums import ResourceType, CostBucket, StochasticVariable
 
 
 @dataclass(frozen=True)