feat: add bash completion generation for command line interface

- Add --generate-bash-completion flag to output bash completion script
- Provide intelligent completions for config files (*.json) and message counts
- Support tab completion for all available command line options
- Generate professional script with proper comments and error handling

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

go/config/config.go

@@ -96,8 +96,9 @@ func ParseCommandLine() *CommandLineArgs {
 	pflag.StringVarP(&args.ConfigPath, "config", "c", "", "Path to configuration file")
 	pflag.IntVarP(&args.MaxMessages, "max-messages", "m", 0, "Maximum number of messages to process per mailbox per run (0 = no limit)")
 
-	// Add help option
+	// Add utility options
 	pflag.BoolP("help", "h", false, "Show help message")
+	pflag.Bool("generate-bash-completion", false, "Generate bash completion script and exit")
 
 	pflag.Parse()
 
@@ -110,9 +111,61 @@ func ParseCommandLine() *CommandLineArgs {
 		os.Exit(0)
 	}
 
+	// Handle bash completion generation
+	if generateCompletion, _ := pflag.CommandLine.GetBool("generate-bash-completion"); generateCompletion {
+		GenerateBashCompletion()
+		os.Exit(0)
+	}
+
 	return &args
 }
 
+// GenerateBashCompletion generates a bash completion script for mail2couch
+func GenerateBashCompletion() {
+	appName := filepath.Base(os.Args[0])
+	script := fmt.Sprintf(`#!/bin/bash
+# Bash completion script for %s
+# Generated automatically by %s --generate-bash-completion
+
+_%s_completions() {
+    local cur prev words cword
+    _init_completion || return
+
+    case $prev in
+        -c|--config)
+            # Complete config files (*.json)
+            _filedir "json"
+            return
+            ;;
+        -m|--max-messages)
+            # Complete with numbers, suggest common values
+            COMPREPLY=($(compgen -W "10 50 100 500 1000" -- "$cur"))
+            return
+            ;;
+    esac
+
+    if [[ $cur == -* ]]; then
+        # Complete with available options
+        local opts="-c --config -m --max-messages -h --help --generate-bash-completion"
+        COMPREPLY=($(compgen -W "$opts" -- "$cur"))
+        return
+    fi
+
+    # No default completion for other cases
+}
+
+# Register the completion function
+complete -F _%s_completions %s
+
+# Enable completion for common variations of the command name
+if [[ "$(%s --help 2>/dev/null)" =~ "mail2couch" ]]; then
+    complete -F _%s_completions mail2couch
+fi
+`, appName, appName, appName, appName, appName, appName, appName)
+
+	fmt.Print(script)
+}
+
 // FindConfigFile searches for config.json in the following order:
 // 1. Path specified by --config/-c flag
 // 2. ./config.json (current directory)