Strip git format-patch footer before parsing

[Copilot]

git format-patch appends an email signature footer (-- \n<version>) to patch files. The -- line was incorrectly parsed as a deletion in the diff view.

Changes

• Add stripGitPatchFooter() to remove the footer before passing content to diff2html
• Regex matches footer at EOF: \n-- \n<semver>...\n?$

Example footer stripped

@@ -1,3 +1,3 @@
 Hello
-World
+Universe
-- 
2.43.0

The regex only matches footers at end-of-file, preserving legitimate -- deletion lines within diffs.

Original prompt

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This section details on the original issue you should resolve

<issue_title>问题修复</issue_title>
<issue_description>git format-patch 生成的patch文件中，底部会有

- -
git版本号

在解析时会将 - - 也作为差分显示出来，请修复这个问题</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes 问题修复 #33

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