chore: go mod tidy (#20)

Remove ~95 lines of stale linter-chain duplicates from go.sum and one
unused indirect (jingyugao/rowserrcheck) from go.mod. No code changes;
running tools (just ready / golangci-lint) was leaving the working
tree dirty because tidy reconciled the cruft on every invocation.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: retr0h

go.mod

@@ -118,7 +118,6 @@ require (
 	github.com/hexops/gotextdiff v1.0.3 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/jgautheron/goconst v1.10.0 // indirect
-	github.com/jingyugao/rowserrcheck v1.1.1 // indirect
 	github.com/jjti/go-spancheck v0.6.5 // indirect
 	github.com/julz/importas v0.2.0 // indirect
 	github.com/karamaru-alpha/copyloopvar v1.2.2 // indirect