feat: implement real IMAP message parsing with native CouchDB attachments

- Replace placeholder message generation with actual IMAP message fetching using go-message library
- Add per-account CouchDB databases for better organization and isolation
- Implement native CouchDB attachment storage with proper revision management
- Add command line argument parsing with --max-messages flag for controlling message processing limits
- Support both sync and archive modes with proper document synchronization
- Add comprehensive test environment with Podman containers (GreenMail IMAP server + CouchDB)
- Implement full MIME multipart parsing for proper body and attachment extraction
- Add TLS and plain IMAP connection support based on port configuration
- Update configuration system to support sync vs archive modes
- Create test scripts and sample data for development and testing

Key technical improvements:
- Real email envelope and header processing with go-imap v2 API
- MIME Content-Type and Content-Disposition parsing for attachment detection
- CouchDB document ID generation using mailbox_uid format for uniqueness
- Duplicate detection and prevention to avoid re-storing existing messages
- Proper error handling and connection management for IMAP operations

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

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

test/dovecot/users

@@ -0,0 +1,8 @@
+# User database for Dovecot testing
+# Format: username:uid:gid:home:shell
+
+# Test user accounts
+testuser1::1001:1001:/var/mail/testuser1::
+testuser2::1002:1002:/var/mail/testuser2::
+syncuser::1003:1003:/var/mail/syncuser::
+archiveuser::1004:1004:/var/mail/archiveuser::