Migrate from Flask to FastAPI and Upgrade SQLAlchemy to 2.0+

[S0okJu]

Changes

• Framework Migration: Migrated from Flask to FastAPI

  • Updated route definitions to use FastAPI decorators and dependency injection
  • Replaced Flask request handling with FastAPI's automatic request/response models

• SQLAlchemy Upgrade: Upgraded to SQLAlchemy >= 2.0

  • Migrated to SQLAlchemy 2.0 syntax and patterns
  • Updated query syntax from legacy to modern style
  • Refactored model definitions to use new declarative patterns
  • Updated session management and connection handling

Migration notes

• All existing functionality has been preserved.
• Database xschema remains unchanged.

Test Scope/Change impact

• unit tests updated and passing
• integration tests updated and passing