feat: add shell completion script

This commit introduces a new `completion` command that provides shell
completion for bash, zsh, and fish.

The completion is implemented as a shell script in `bin/completion.sh`
and the main `mole` script has been updated to use it.

This approach was chosen to keep the completion logic in shell script,
as the `mole` command is primarily a set of shell scripts.

bin/completion.sh

@@ -0,0 +1,92 @@
+#!/bin/bash
+
+case "$1" in
+    bash)
+        cat << 'EOF'
+_mole_completions()
+{
+    local cur_word prev_word
+    cur_word="${COMP_WORDS[COMP_CWORD]}"
+    prev_word="${COMP_WORDS[COMP_CWORD-1]}"
+
+    if [ "$COMP_CWORD" -eq 1 ]; then
+        COMPREPLY=( $(compgen -W "optimize clean uninstall analyze status purge touchid update remove help version completion" -- "$cur_word") )
+    else
+        case "$prev_word" in
+            completion)
+                COMPREPLY=( $(compgen -W "bash zsh fish" -- "$cur_word") )
+                ;;
+            *)
+                COMPREPLY=()
+                ;;
+        esac
+    fi
+}
+
+complete -F _mole_completions mole
+EOF
+        ;;
+    zsh)
+        cat << 'EOF'
+#compdef mole
+
+_mole() {
+    local -a subcommands
+    subcommands=(
+        'optimize:Free up disk space'
+        'clean:Remove apps completely'
+        'uninstall:Check and maintain system'
+        'analyze:Explore disk usage'
+        'status:Monitor system health'
+        'purge:Remove old project artifacts'
+        'touchid:Configure Touch ID for sudo'
+        'update:Update to latest version'
+        'remove:Remove Mole from system'
+        'help:Show help'
+        'version:Show version'
+        'completion:Generate shell completions'
+    )
+    _describe 'subcommand' subcommands
+}
+
+_mole
+EOF
+        ;;
+    fish)
+        cat << 'EOF'
+complete -c mole -n "__fish_mole_no_subcommand" -a optimize -d "Free up disk space"
+complete -c mole -n "__fish_mole_no_subcommand" -a clean -d "Remove apps completely"
+complete -c mole -n "__fish_mole_no_subcommand" -a uninstall -d "Check and maintain system"
+complete -c mole -n "__fish_mole_no_subcommand" -a analyze -d "Explore disk usage"
+complete -c mole -n "__fish_mole_no_subcommand" -a status -d "Monitor system health"
+complete -c mole -n "__fish_mole_no_subcommand" -a purge -d "Remove old project artifacts"
+complete -c mole -n "__fish_mole_no_subcommand" -a touchid -d "Configure Touch ID for sudo"
+complete -c mole -n "__fish_mole_no_subcommand" -a update -d "Update to latest version"
+complete -c mole -n "__fish_mole_no_subcommand" -a remove -d "Remove Mole from system"
+complete -c mole -n "__fish_mole_no_subcommand" -a help -d "Show help"
+complete -c mole -n "__fish_mole_no_subcommand" -a version -d "Show version"
+complete -c mole -n "__fish_mole_no_subcommand" -a completion -d "Generate shell completions"
+
+complete -c mole -n "not __fish_mole_no_subcommand" -a bash -d "generate bash completion" -n "__fish_see_subcommand_path completion"
+complete -c mole -n "not __fish_mole_no_subcommand" -a zsh -d "generate zsh completion" -n "__fish_see_subcommand_path completion"
+complete -c mole -n "not __fish_mole_no_subcommand" -a fish -d "generate fish completion" -n "__fish_see_subcommand_path completion"
+
+function __fish_mole_no_subcommand
+    for i in (commandline -opc)
+        if contains -- $i optimize clean uninstall analyze status purge touchid update remove help version completion
+            return 1
+        end
+    end
+    return 0
+end
+
+function __fish_see_subcommand_path
+    string match -q -- "completion" (commandline -opc)[1]
+end
+EOF
+        ;;
+    *)
+        echo "Usage: mole completion [bash|zsh|fish]"
+        exit 1
+        ;;
+esac