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/remove-git-folder

@@ -1,7 +1,7 @@
 #!/bin/bash
 
 remove-git-folder() {
-    if [[ -z "$1" ]]; then echo "\$1 is empty."; exit; fi
+    if [[ -z "$1" ]]; then echo "\$1/path is empty."; exit; fi
     local git_folders=$(ls-git-folder "$1")
 
     echo "Delete: $git_folders"