重构：使用PlanStepStatus枚举替代硬编码status

[rxdaozhang]

This pull request introduces a new PlanStepStatus enum class to standardize the statuses of plan steps and updates the codebase to use this enum instead of hardcoded status strings. The changes improve code readability and maintainability by centralizing the status definitions and related utility methods.

Key changes include:

Introduction of PlanStepStatus Enum:

• app/flow/base.py: Added PlanStepStatus enum class with possible statuses (NOT_STARTED, IN_PROGRESS, COMPLETED, BLOCKED) and utility methods (get_all_statuses, get_active_statuses, get_status_marks).

Refactoring to Use PlanStepStatus:

• app/flow/planning.py: Updated imports to include PlanStepStatus.
• app/flow/planning.py: Replaced hardcoded status strings with PlanStepStatus values in _get_current_step_info, _mark_step_completed, and _generate_plan_text_from_storage methods. [1] [2] [3] [4] [5] [6]Features

• Feature 1
• Feature 2

Feature Docs

Influence

Result

Other

[mannaandpoem]

LGTM