feat: standardize required/optional param notation and update error messages

- Updated `task`, `task.template`, and `library.md` to use angle brackets (`<param>`) for required parameters and square brackets (`[param]`) for optional ones.
- Fixed argument order mismatches in `create-symlink`, `create-symlink-files`, and `commit-git-folder` documentation.
- Removed non-existent `[path]` parameter from `merge-git-remote`.
- Standardized empty-argument error messages across `bin/*` scripts to use slash notation (e.g., `$1/path is empty.`).
- Updated prompt file `prompts/21_show-optional-and-required-params-in-task-help.md` to mark task as completed and log work.

bin/switch-git-folder

@@ -2,7 +2,7 @@
 
 switch-git-folder() {
     if [[ -z "$1" ]]; then
-        echo '$1/path is empty.'
+        echo '$1/branch is empty.'
         exit
     fi
     if [[ -z "$2" ]]; then