fix: use signal-based diff acceptance instead of direct file writes

Fixes #33

- Change from direct file writing to signal-based communication with Claude Code
- Plugin sends acceptance signal, Claude Code handles actual file modifications
- Plugin reloads buffers after Claude Code completes file writes
- Unified behavior for both <leader>da keymap and :w command
- Clean up verbose debug logging and outdated comments

Previously the plugin was directly writing to files when accepting diffs,
which could cause issues. Now the plugin properly delegates file modifications
to Claude Code through signal-based acceptance.

Change-Id: Iae72c91da515c4167590cea75d123ff30d10c5f8
Signed-off-by: Thomas Kosiewski <tk@coder.com>

Author: ThomasK33