Go's semantic import versioning requires v2+ modules to include the
major version in the module path. This enables using proper version
tags (v3.x.x) instead of pseudo-versions.
Updated module path: code.gitcaddy.com/server/v3
Fix the swagger documentation for the `diffpatch` API endpoint,
and fix the wrong API path caused by a refactoring change.
Closes#35602
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Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>