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/populate-greenmail.py

@@ -0,0 +1,129 @@
+#!/usr/bin/env python3
+
+import imaplib
+import email
+from email.mime.text import MIMEText
+from email.mime.multipart import MIMEMultipart
+from email.mime.base import MIMEBase
+from email import encoders
+import time
+import sys
+
+def create_simple_message(subject, body, from_addr="test-sender@example.com"):
+    """Create a simple text message"""
+    msg = MIMEText(body)
+    msg['Subject'] = subject
+    msg['From'] = from_addr
+    msg['Date'] = email.utils.formatdate(localtime=True)
+    return msg.as_string()
+
+def create_message_with_attachment(subject, body, attachment_content, from_addr="test-sender@example.com"):
+    """Create a message with an attachment"""
+    msg = MIMEMultipart()
+    msg['Subject'] = subject
+    msg['From'] = from_addr
+    msg['Date'] = email.utils.formatdate(localtime=True)
+    
+    # Add body
+    msg.attach(MIMEText(body, 'plain'))
+    
+    # Add attachment
+    part = MIMEBase('text', 'plain')
+    part.set_payload(attachment_content)
+    encoders.encode_base64(part)
+    part.add_header('Content-Disposition', 'attachment; filename="attachment.txt"')
+    msg.attach(part)
+    
+    return msg.as_string()
+
+def populate_user_mailbox(username, password, host='localhost', port=3143):
+    """Populate a user's mailbox with test messages"""
+    print(f"Connecting to {username}@{host}:{port}")
+    
+    try:
+        # Connect to IMAP server
+        imap = imaplib.IMAP4(host, port)
+        imap.login(username, password)
+        imap.select('INBOX')
+        
+        print(f"Creating messages for {username}...")
+        
+        # Create 10 regular messages
+        for i in range(1, 11):
+            if i % 3 == 0:
+                # Every 3rd message has attachment
+                msg = create_message_with_attachment(
+                    f"Test Message {i} with Attachment",
+                    f"This is test message {i} for {username} with an attachment.",
+                    f"Sample attachment content for message {i}"
+                )
+                print(f"  Created message {i} (with attachment)")
+            else:
+                # Simple message
+                msg = create_simple_message(
+                    f"Test Message {i}",
+                    f"This is test message {i} for {username}."
+                )
+                print(f"  Created message {i}")
+            
+            # Append message to INBOX
+            imap.append('INBOX', None, None, msg.encode('utf-8'))
+            time.sleep(0.1)  # Small delay to avoid overwhelming
+        
+        # Create additional test messages
+        special_messages = [
+            ("Important Message", "This is an important message for testing sync/archive modes."),
+            ("Message with Special Characters", "This message contains special characters: äöü ñ 中文 🚀")
+        ]
+        
+        for subject, body in special_messages:
+            msg = create_simple_message(subject, body)
+            imap.append('INBOX', None, None, msg.encode('utf-8'))
+            print(f"  Created special message: {subject}")
+        
+        imap.logout()
+        print(f"✅ Successfully created 12 messages for {username}")
+        return True
+        
+    except Exception as e:
+        print(f"❌ Error populating {username}: {e}")
+        return False
+
+def main():
+    print("🚀 Populating GreenMail with test messages using IMAP...")
+    
+    # Test accounts
+    accounts = [
+        ("testuser1", "password123"),
+        ("testuser2", "password456"), 
+        ("syncuser", "syncpass"),
+        ("archiveuser", "archivepass")
+    ]
+    
+    # Wait for GreenMail to be ready
+    print("Waiting for GreenMail to be ready...")
+    time.sleep(5)
+    
+    success_count = 0
+    for username, password in accounts:
+        if populate_user_mailbox(username, password):
+            success_count += 1
+        time.sleep(1)  # Brief pause between accounts
+    
+    print(f"\n🎉 Successfully populated {success_count}/{len(accounts)} accounts!")
+    
+    if success_count == len(accounts):
+        print("\n✅ All test accounts ready:")
+        for username, password in accounts:
+            print(f"  - {username}:{password}@localhost")
+        print(f"\nGreenMail Services:")
+        print(f"  - IMAP: localhost:3143")
+        print(f"  - IMAPS: localhost:3993") 
+        print(f"  - SMTP: localhost:3025")
+        return 0
+    else:
+        print(f"\n❌ Failed to populate {len(accounts) - success_count} accounts")
+        return 1
+
+if __name__ == "__main__":
+    sys.exit(main())