Port diff_tool.py to Go

[Copilot]

Reimplements diff_tool.py in Go with identical runtime behavior: reads config.json, loads a language file, prompts interactively for target repo / commit range / output path, diffs changed files, and writes a syntax-highlighted .docx report.

Library mapping

Python	Go
python-docx	github.com/fumiama/go-docx
pygments	github.com/alecthomas/chroma/v2
difflib.SequenceMatcher	github.com/sergi/go-diff/diffmatchpatch (line-mode)
pathspec	github.com/sabhiram/go-gitignore
PIL	stdlib image

Key implementation notes

• Config defaults pre-populated before json.Unmarshal so absent keys behave exactly as Python's config.get(key, default).
• Pygments → Chroma style mapping: "default" is remapped to "pygments" (chroma's equivalent).
• Cell borders: Python's parse_xml-based border removal is replicated by setting WTableBorder{Val: "nil"} on specific sides of each WTableCellProperties.TableBorders.
• Empty tree SHA: 4b825dc642cb6eb9a060e54bf8d69288fbee4904 used when include_first_commit=true and commit1 is the repo's root commit, so all lines appear as additions.
• open_after_creation: cross-platform (cmd /c start / open / xdg-open).
• xml:space="preserve" set on every <w:t> node to retain code indentation in the generated document.

Original prompt

port the diff_tool.py to golang with exactly the same behavior

The user has attached the following files from their workspace:

• diff_tool.py

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