More color fixes (#29)

* update readme

* Fix merge conflict coloring on side panes and empty lines

- Add source marks for conflict backgrounds (visible on empty lines
  unlike paragraph_background tags in GTK4)
- Compute merged conflict regions from middle pane to correctly detect
  which side-pane chunks fall within conflict zones
- Absorb equal gaps within conflict regions regardless of size so
  side-pane conflict bands match the middle pane
- Skip filler lines inside conflict bands to avoid stray colored lines
- Update diff tag colors on scheme change for dark/light awareness
- Fix README merge tool config to use --global flag

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Brighten dark-mode diff colors for readability

Previous dark values were too subtle and blended into dark backgrounds,
making diffs hard to read especially on macOS. Increase brightness of
chunk backgrounds, inline highlights, strokes, bands, and search colors.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* bump to 0.5.4

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: joske

Cargo.lock

@@ -1,6 +1,6 @@
 [package]
 name = "mergers"
-version = "0.5.3"
+version = "0.5.4"
 edition = "2024"
 description = "A visual diff and merge tool for files and directories"
 license = "GPL-2.0"

Cargo.toml

@@ -96,9 +96,9 @@ mergers file1.txt file2.txt -L "Original" -L "Modified"
 To use mergers as your git merge tool:
 
 ```bash
-git config merge.tool mergers
-git config mergetool.mergers.cmd 'mergers "$LOCAL" "$MERGED" "$REMOTE"'
-git config mergetool.mergers.trustExitCode true
+git config --global merge.tool mergers
+git config --global mergetool.mergers.cmd 'mergers "$LOCAL" "$MERGED" "$REMOTE"'
+git config --global mergetool.mergers.trustExitCode true
 ```
 
 Then resolve conflicts with: