feat: implement comprehensive wildcard folder selection and keyword filtering

## Wildcard Folder Selection
- Add support for wildcard patterns (`*`, `?`, `[abc]`) using filepath.Match
- Implement special case: `"*"` selects ALL available folders
- Support for complex include/exclude pattern combinations
- Maintain backwards compatibility with exact string matching
- Enable subfolder pattern matching (e.g., `Work/*`, `*/Drafts`)

## Keyword Filtering
- Add SubjectKeywords, SenderKeywords, RecipientKeywords to MessageFilter config
- Implement case-insensitive keyword matching across message fields
- Support multiple keywords per filter type with inclusive OR logic
- Add ShouldProcessMessage method for message-level filtering

## Enhanced Test Environment
- Create comprehensive wildcard pattern test scenarios
- Add 12 test folders covering various pattern types: Work/*, Important/*, Archive/*, exact matches
- Implement dedicated wildcard test script (test-wildcard-patterns.sh)
- Update test configurations to demonstrate real-world wildcard usage patterns
- Enhance test data generation with folder-specific messages for validation

## Documentation
- Create FOLDER_PATTERNS.md with comprehensive wildcard examples and use cases
- Update CLAUDE.md to reflect all implemented features and current status
- Enhance test README with detailed wildcard pattern explanations
- Provide configuration examples for common email organization scenarios

## Message Origin Tracking
- Verify all messages in CouchDB properly tagged with origin folder in `mailbox` field
- Maintain per-account database isolation for better organization
- Document ID format: `{folder}_{uid}` ensures uniqueness across folders

Key patterns supported:
- `["*"]` - All folders (with excludes)
- `["Work*", "Important*"]` - Prefix matching
- `["Work/*", "Archive/*"]` - Subfolder patterns
- `["INBOX", "Sent"]` - Exact matches
- Complex include/exclude combinations

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

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

CLAUDE.md

@@ -67,7 +67,7 @@ The application uses `config.json` for configuration with the following structur
   - `mode`: Either "sync" or "archive" (defaults to "archive" if not specified)
     - **sync**: 1-to-1 relationship - CouchDB documents match exactly what's in the mail account (may remove documents from CouchDB)
     - **archive**: Archive mode - CouchDB keeps all messages ever seen, even if deleted from mail account (never removes documents)
-  - Filtering options for folders and messages
+  - Filtering options for folders and messages with wildcard support
   - Enable/disable per source
 
 ### Configuration File Discovery
@@ -90,13 +90,16 @@ This design ensures the same `config.json` format will work for both Go and Rust
 - ✅ Build error fixes
 - ✅ Email message retrieval framework (with placeholder data)
 - ✅ Email storage to CouchDB framework with native attachments
-- ✅ Folder filtering logic
+- ✅ Folder filtering logic with wildcard support (`*`, `?`, `[abc]` patterns)
 - ✅ Date filtering support
+- ✅ Keyword filtering support (subject, sender, recipient keywords)
 - ✅ Duplicate detection and prevention
 - ✅ Sync vs Archive mode implementation
 - ✅ CouchDB attachment storage for email attachments
-- ❌ Real IMAP message parsing (currently uses placeholder data)
-- ❌ Full message body and attachment handling
+- ✅ Real IMAP message parsing with go-message library
+- ✅ Full message body and attachment handling with MIME multipart support
+- ✅ Command line argument support (--max-messages flag)
+- ✅ Per-account CouchDB databases for better organization
 - ❌ Incremental sync functionality
 - ❌ Rust implementation