servicepack v1.2.18 — the update rewrites only what it delivered

No Go code change.

The update rewrites servicepack's import path to yours after syncing. That
rewrite was a `find` over the whole working tree, and find does not honour
.gitignore -- so it edited *.go and *.mod inside scratch dirs and nested clones,
invisibly, because the damage was all ignored. One project saw 62,026 files
visited instead of ~50, and an unrelated servicepack checkout under the repo had
its imports rewritten.

It is now scoped to rsync's own transfer manifest: the exact set the sync
delivered, after every exclude and .servicepackupdateignore entry. The companion
*.mod walk is gone -- go.mod is handled directly, by the upgrade-only dependency
merge, and by `make dep`.

A missing manifest now aborts rather than silently skipping, and a post-rewrite
scan warns if anything the repo actually owns still references the framework
path.

Both scripts run from the freshly downloaded framework, so this lands on the
very next `make servicepack-update` -- no intermediate release needed.