Add feature file and Behave steps covering all reachable code paths in
merge_conflict.py: MODIFY_MODIFY/DELETE/ADD_ADD conflict types, auto-
resolution for MODIFY_DELETE/DELETE_MODIFY/convergent ADD_ADD, DELETE_DELETE
absence, detect_diff_text formatting, describe_all status types, and direct
_analyse_field call for the unreachable ADD_ADD branch.
Restores coverage above the 96.5% threshold after the merge_conflict module
was added with zero test coverage.
ISSUES CLOSED: #11000
- Remove unused `noqa: F401` from planconfig __init__.py (lint RUF100)
- Fix `auto_resolved` field default_factory: list → dict to match
declared type `dict[str, str | None]` (typecheck reportAssignmentType)