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/project.py

@@ -1,9 +1,10 @@
 from __future__ import annotations
 
 from datetime import datetime
-from enum import Enum
 from typing import TYPE_CHECKING, List
 
+from .enums import MiningOperationType
+
 from sqlalchemy import DateTime, Enum as SQLEnum, ForeignKey, Integer, String, Text
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 from sqlalchemy.sql import func
@@ -15,16 +16,6 @@ if TYPE_CHECKING:  # pragma: no cover
     from .pricing_settings import PricingSettings
 
 
-class MiningOperationType(str, Enum):
-    """Supported mining operation categories."""
-
-    OPEN_PIT = "open_pit"
-    UNDERGROUND = "underground"
-    IN_SITU_LEACH = "in_situ_leach"
-    PLACER = "placer"
-    QUARRY = "quarry"
-    MOUNTAINTOP_REMOVAL = "mountaintop_removal"
-    OTHER = "other"
 
 
 class Project(Base):
@@ -36,7 +27,9 @@ class Project(Base):
     name: Mapped[str] = mapped_column(String(255), nullable=False, unique=True)
     location: Mapped[str | None] = mapped_column(String(255), nullable=True)
     operation_type: Mapped[MiningOperationType] = mapped_column(
-        SQLEnum(MiningOperationType), nullable=False, default=MiningOperationType.OTHER
+        SQLEnum(MiningOperationType, name="miningoperationtype", create_type=False),
+        nullable=False,
+        default=MiningOperationType.OTHER,
     )
     description: Mapped[str | None] = mapped_column(Text, nullable=True)
     pricing_settings_id: Mapped[int | None] = mapped_column(