feat: implement complete Rust version of mail2couch

- Add comprehensive Rust implementation matching Go functionality
- Configuration loading with automatic file discovery
- GNU-style command line parsing with clap (--config/-c, --max-messages/-m)
- CouchDB client integration with document storage and sync metadata
- IMAP client functionality with message fetching and parsing
- Folder filtering with wildcard pattern support (*, ?, [abc])
- Message filtering by subject, sender, and recipient keywords
- Incremental sync functionality with metadata tracking
- Bash completion generation matching Go implementation
- Cross-compatible document schemas and database structures
- Successfully tested with existing test environment

Note: TLS support and advanced email parsing features pending

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

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

rust/src/cli.rs

@@ -0,0 +1,119 @@
+//! Command line interface for mail2couch
+//! 
+//! This module handles command line argument parsing and bash completion generation,
+//! matching the behavior of the Go implementation.
+
+use clap::{Arg, ArgAction, Command};
+use std::env;
+use std::path::Path;
+
+use crate::config::CommandLineArgs;
+
+/// Parse command line arguments using GNU-style options
+pub fn parse_command_line() -> CommandLineArgs {
+    let app = Command::new("mail2couch")
+        .version(env!("CARGO_PKG_VERSION"))
+        .about("Email backup utility for CouchDB")
+        .long_about("A powerful email backup utility that synchronizes mail from IMAP accounts to CouchDB databases with intelligent incremental sync, comprehensive filtering, and native attachment support.")
+        .arg(Arg::new("config")
+            .short('c')
+            .long("config")
+            .value_name("FILE")
+            .help("Path to configuration file")
+            .action(ArgAction::Set))
+        .arg(Arg::new("max-messages")
+            .short('m')
+            .long("max-messages")
+            .value_name("N")
+            .help("Maximum number of messages to process per mailbox per run (0 = no limit)")
+            .value_parser(clap::value_parser!(u32))
+            .action(ArgAction::Set))
+        .arg(Arg::new("generate-bash-completion")
+            .long("generate-bash-completion")
+            .help("Generate bash completion script and exit")
+            .action(ArgAction::SetTrue));
+
+    let matches = app.get_matches();
+
+    // Handle bash completion generation
+    if matches.get_flag("generate-bash-completion") {
+        generate_bash_completion();
+        std::process::exit(0);
+    }
+
+    CommandLineArgs {
+        config_path: matches.get_one::<String>("config").map(|s| s.clone()),
+        max_messages: matches.get_one::<u32>("max-messages").copied(),
+        generate_bash_completion: matches.get_flag("generate-bash-completion"),
+        help: false, // Using clap's built-in help
+    }
+}
+
+/// Generate bash completion script for mail2couch
+pub fn generate_bash_completion() {
+    let app_name = env::args().next()
+        .map(|path| {
+            Path::new(&path).file_name()
+                .and_then(|name| name.to_str())
+                .unwrap_or("mail2couch")
+                .to_string()
+        })
+        .unwrap_or_else(|| "mail2couch".to_string());
+
+    let script = format!(r#"#!/bin/bash
+# Bash completion script for {}
+# Generated automatically by {} --generate-bash-completion
+
+_{}_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 _{}_completions {}
+
+# Enable completion for common variations of the command name
+if [[ "$({} --help 2>/dev/null)" =~ "mail2couch" ]]; then
+    complete -F _{}_completions mail2couch
+fi
+"#, app_name, app_name, app_name, app_name, app_name, app_name, app_name);
+
+    print!("{}", script);
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_bash_completion_generation() {
+        // Test that bash completion generation doesn't panic
+        // This is a basic smoke test
+        let _output = std::panic::catch_unwind(|| {
+            generate_bash_completion();
+        });
+        // Just verify it doesn't panic, we can't easily test the output without capturing stdout
+    }
+}