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.

pyproject.toml

@@ -27,7 +27,6 @@ branch = true
 source = ["."]
 omit = [
   "tests/*",
-  "alembic/*",
   "scripts/*",
   "main.py",
   "routes/reports.py",
@@ -39,6 +38,6 @@ skip_empty = true
 show_missing = true
 
 [tool.bandit]
-exclude_dirs = ["alembic", "scripts"]
+exclude_dirs = ["scripts"]
 skips = ["B101", "B601"]  # B101: assert_used, B601: shell_injection (may be false positives)