refactor: replace empty slice literal with var

An empty slice can be represented by `nil` or an empty slice literal. They are
functionally equivalent — their `len` and `cap` are both zero — but the `nil`
slice is the preferred style. For more information about empty slices,
see [Declaring Empty Slices](https://github.com/golang/go/wiki/CodeReviewComments#declaring-empty-slices).

pkg/building/posts.go

@@ -232,7 +232,7 @@ func getThreadPosts(thread *gcsql.Thread) ([]Post, error) {
 
 func GetRecentPosts(boardid int, limit int) ([]Post, error) {
 	query := postQueryBase
-	args := []any{}
+	var args []any
 
 	if boardid > 0 {
 		query += " WHERE t.board_id = ?"

pkg/manage/actions.go

@@ -86,7 +86,8 @@ func RegisterManagePage(id string, title string, permissions int, jsonOutput int
 }
 
 func getAvailableActions(rank int, noJSON bool) []Action {
-	available := []Action{}
+	var available []Action
+
 	for _, action := range actions {
 		if (rank < action.Permissions || action.Permissions == NoPerms) ||
 			(noJSON && action.JSONoutput == AlwaysJSON) {

pkg/posting/reports.go

@@ -23,7 +23,8 @@ func HandleReport(request *http.Request) error {
 	if request.Method != "POST" {
 		return ErrInvalidReport
 	}
-	reportedPosts := []int{}
+	var reportedPosts []int
+
 	var id int
 	if !gcsql.DoesBoardExistByDir(board) {
 		return gcsql.ErrBoardDoesNotExist