fix: preserve original file line endings during edits

[akramcodez]

Description

EditTool was converting all CRLF line endings to LF during file edits, causing entire files to show as changed in Git even when only a single line was modified. This created friction for Windows and cross-platform teams.

Solution

• Detect original line ending before normalization
• Process edits with LF internally (existing behavior)
• Restore original line ending format when writing file back
• New files default to LF

Changes

• edit.ts: Added line ending detection and restoration logic

Testing

• CRLF files maintain CRLF after edits
• LF files maintain LF after edits
• Internal processing remains consistent with LF
• New files use LF by default

fixes #11