Move scripts to Nix files

Move the scripts I commonly use into Nix files managed by Home Manager.

Some, like `mounter` and `unmounter` are desktop-only, but this can be
addressed in a future commit to create per-host scripts or
desktop/non-desktop scripts.

This commit also removes a number of unused scripts that are either
included in packages like `git-extras` or aren't used.

modules/home-manager/cli/scripts/update-all-git-repos.nix

@@ -0,0 +1,33 @@
+{ pkgs }:
+
+pkgs.writeShellApplication {
+  name = "update-all-git-repos";
+
+  runtimeInputs = with pkgs; [
+    findutils
+    git
+  ];
+
+  text = ''
+    # Update all top-level Git repository clones within my Code directories to their
+    # latest version.
+
+    dirs=$(find "$XDG_REPOS_DIR" -mindepth 2 -maxdepth 3 -type d -name .git -not -path '*/*.old/*')
+
+    for dir in $dirs; do
+      repo_path="''${dir%/.git}"
+
+      cd "''${repo_path}"
+
+      # If the repo is a bare clone, the commands need to be run within the
+      # worktree directory.
+      [[ -f .bare/worktrees/main/gitdir && -d main && -f main/.git ]] && cd main
+
+      echo "Updating $(pwd)"
+
+      # Update the repository.
+      git fetch --all --jobs=4 --progress --prune
+      git pull --rebase
+    done
+  '';
+}