style💄: run gofmt over the tree

`gofmt -l` listed 26 files. Seventeen of them were missing the newline at the
end of the file; the rest are indentation that used spaces where the file uses
tabs, a handful of call sites written `f(a,b)`, and the doc comment spacing
gofmt has rewritten since 1.19 (`//X` to `// X`).

Nothing here changes behaviour: `go build ./...` and `go vet ./...` are clean
and `go test ./common/...` passes, which is the half of the tree these files
are concentrated in.

Only the files gofmt named are touched, so the diff reads line by line rather
than as a reflow of the whole repository. `gofmt -l` is now empty, which is the
precondition for gating it in CI -- worth doing, but a separate change.

cmd/api/demo.go

@@ -5,4 +5,4 @@ import "go-admin/app/demo/router"
 func init() {
 	//注册路由 fixme 其他应用的路由，在本目录新建文件放在init方法
 	AppRouters = append(AppRouters, router.InitRouter)
-}
+}