feat: add --dry-run mode to Go implementation

Add comprehensive dry-run functionality that allows users to test their
configuration without making any changes to CouchDB. The feature includes:

- New --dry-run/-n command line flag with help and completion support
- Skips all CouchDB write operations while preserving IMAP operations
- Provides detailed logging of what would be done in normal mode
- Shows sample message data and metadata updates that would occur
- Maintains all existing functionality when dry-run is disabled

This addresses the critical usability need identified in ANALYSIS.md for
safe configuration testing before making database changes.

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

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

go/config/config.go

@@ -86,6 +86,7 @@ func (ms *MailSource) IsArchiveMode() bool {
 type CommandLineArgs struct {
 	ConfigPath  string
 	MaxMessages int
+	DryRun      bool
 }
 
 // ParseCommandLine parses command line arguments using GNU-style options
@@ -95,6 +96,7 @@ func ParseCommandLine() *CommandLineArgs {
 	// Define long options with -- and short options with -
 	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)")
+	pflag.BoolVarP(&args.DryRun, "dry-run", "n", false, "Show what would be done without making any changes")
 
 	// Add utility options
 	pflag.BoolP("help", "h", false, "Show help message")
@@ -146,7 +148,7 @@ _%s_completions() {
 
     if [[ $cur == -* ]]; then
         # Complete with available options
-        local opts="-c --config -m --max-messages -h --help --generate-bash-completion"
+        local opts="-c --config -m --max-messages -n --dry-run -h --help --generate-bash-completion"
         COMPREPLY=($(compgen -W "$opts" -- "$cur"))
         return
     fi
@@ -217,5 +219,8 @@ func LoadConfigWithDiscovery(args *CommandLineArgs) (*Config, error) {
 	} else {
 		fmt.Printf("Maximum messages per mailbox: unlimited\n")
 	}
+	if args.DryRun {
+		fmt.Printf("DRY-RUN MODE: No changes will be made to CouchDB\n")
+	}
 	return LoadConfig(configPath)
 }