Rename the module to the Coffey-Labs organisation

The repositories moved off LINUXexpert-org. Here that is not a
documentation change: the old organisation was the module path, so it is
declared in go.mod and repeated in every internal import.

Leaving it would have been worse than a stale link. GitHub redirects the
repository, but a go.mod whose module line disagrees with the path it was
fetched from is an error rather than a redirect, so `go get` on the new
address would have failed against the old declaration.

go.mod, 34 files of imports, and the repository links in README and
ARCHITECTURE. go mod tidy leaves go.sum untouched -- no dependency moved,
only our own path.

ARCHITECTURE.md

@@ -341,8 +341,8 @@ against an already-migrated store.
   whether the recreated container comes up as the server it was. That is
   what would retire the flag.
 
-  [#9]: https://github.com/LINUXexpert-org/stalwart-migrator/pull/9
-  [#11]: https://github.com/LINUXexpert-org/stalwart-migrator/pull/11
+  [#9]: https://github.com/Coffey-Labs/stalwart-migrator/pull/9
+  [#11]: https://github.com/Coffey-Labs/stalwart-migrator/pull/11
 - Quota recalculation is the one step allowed to fail without failing the
   phase. Stale counters are an accounting problem; a failed cutover is one
   an operator has to respond to by restoring a machine that is otherwise