fix: unify diff acceptance behavior and clean up logging

Fixes #33

- Refactor duplicate code between <leader>da keymap and :w command
- Create unified diff acceptance behavior in _resolve_diff_as_saved
- Remove redundant file I/O operations, use MCP broadcast-only approach
- Clean up verbose debug logging and outdated comments
- Update tests to work with unified approach
- Ensure consistent window management across acceptance methods

The unified approach eliminates code duplication and makes the diff
acceptance behavior more idiomatic and maintainable.

Change-Id: I30f5fdb2af417cd62a197d235f2ca0f5df887e6e
Signed-off-by: Thomas Kosiewski <tk@coder.com>

Author: ThomasK33