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>

config.json

@@ -14,7 +14,7 @@
       "port": 993,
       "user": "your-email@gmail.com",
       "password": "your-app-password",
-      "sync": true,
+      "mode": "archive",
       "folderFilter": {
         "include": ["INBOX", "Sent"],
         "exclude": ["Spam", "Trash"]
@@ -31,7 +31,7 @@
       "port": 993,
       "user": "user@work.com",
       "password": "password",
-      "sync": true,
+      "mode": "sync",
       "folderFilter": {
         "include": [], 
         "exclude": []