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/dovecot.conf

@@ -0,0 +1,79 @@
+# Dovecot configuration for testing mail2couch
+
+# Basic settings
+protocols = imap
+listen = *
+
+# SSL/TLS settings - make optional for easier testing
+ssl = optional
+ssl_cert = </etc/dovecot/ssl/server.crt
+ssl_key = </etc/dovecot/ssl/server.key
+
+# Authentication
+auth_mechanisms = plain login
+disable_plaintext_auth = no
+
+# User database
+passdb {
+  driver = passwd-file
+  args = scheme=plain username_format=%u /etc/dovecot/passwd
+}
+
+userdb {
+  driver = passwd-file
+  args = username_format=%u /etc/dovecot/users
+}
+
+# Mail location
+mail_location = maildir:/var/mail/%u
+
+# Mailbox settings
+namespace inbox {
+  type = private
+  separator = /
+  prefix = 
+  location = 
+  inbox = yes
+  hidden = no
+  list = yes
+  subscriptions = yes
+
+  mailbox Drafts {
+    special_use = \Drafts
+  }
+  mailbox Junk {
+    special_use = \Junk
+  }
+  mailbox Trash {
+    special_use = \Trash
+  }
+  mailbox Sent {
+    special_use = \Sent
+  }
+}
+
+# Services
+service imap-login {
+  inet_listener imap {
+    port = 143
+  }
+  inet_listener imaps {
+    port = 993
+    ssl = yes
+  }
+}
+
+service auth {
+  unix_listener auth-userdb {
+    mode = 0666
+  }
+}
+
+# Logging
+log_path = /dev/stdout
+info_log_path = /dev/stdout
+debug_log_path = /dev/stdout
+
+# Process limits
+default_process_limit = 10
+default_client_limit = 100