Preserve exact hunks across renames

[hzw0813]

Summary

• scope per-file Git diffs for renamed paths to both the previous and current path
• preserve an empty hunk set for pure renames instead of reconstructing the entire destination as newly added
• preserve the minimal edited hunk for rename+modify changes
• add regressions for both pure rename and rename+modify cases
• regenerate tracked dist and document the fix

Why

changedFiles() discovers renames using an unscoped git diff --name-status --find-renames, but then reconstructed each file's zero-context patch using only the destination path. Once the pathspec is restricted to the new path, Git can no longer pair the source and destination, so a renamed file is reinterpreted as a whole-file addition. That overstates file.hunks and can make unchanged call sites appear to be inside changed lines.

The fix supplies both previousPath and path whenever rename/copy metadata provides both identities. A pure rename now has no content hunks, while a rename with one edited line produces exactly that one-line hunk.

Verification

• independently reproduced the old Git pathspec behavior before modifying the repository
• full npm test passed after the fix
• clean npm run clean && npm run build passed
• git diff --check passed
• generated dist/git.* refreshed
• temporary updater workflows removed from the final diff