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/podman-compose.yml

@@ -0,0 +1,38 @@
+version: '3.8'
+
+services:
+  # CouchDB for testing
+  couchdb:
+    image: docker.io/couchdb:3.3
+    container_name: mail2couch_test_couchdb
+    environment:
+      - COUCHDB_USER=admin
+      - COUCHDB_PASSWORD=password
+    ports:
+      - "5984:5984"
+    volumes:
+      - couchdb_data:/opt/couchdb/data
+    networks:
+      - mail2couch_test
+
+  # GreenMail IMAP server for testing
+  greenmail:
+    image: docker.io/greenmail/standalone:2.0.1
+    container_name: mail2couch_test_imap
+    ports:
+      - "3143:3143"   # IMAP
+      - "3993:3993"   # IMAPS
+      - "3025:3025"   # SMTP
+    environment:
+      - GREENMAIL_OPTS=-Dgreenmail.setup.test.all -Dgreenmail.hostname=0.0.0.0 -Dgreenmail.users=testuser1:password123@localhost,testuser2:password456@localhost,syncuser:syncpass@localhost,archiveuser:archivepass@localhost
+    networks:
+      - mail2couch_test
+    depends_on:
+      - couchdb
+
+volumes:
+  couchdb_data:
+
+networks:
+  mail2couch_test:
+    driver: bridge