refactor: remove webmail interface, focus on core mail storage functionality

- Remove obsolete CouchDB design documents (webmail.json, dashboard.json)
- Clean up webmail-related code from couch/couch.go (WebmailViews, CreateWebmailViews, etc.)
- Update documentation to focus on core mail-to-CouchDB storage functionality
- Add Future Plans section describing planned webmail viewer as separate component
- Apply go fmt formatting and ensure code quality standards
- Update test documentation to show raw CouchDB API access patterns
- Remove compiled binary from repository

This refactor simplifies the codebase to focus on its core purpose: efficiently
backing up emails from IMAP to CouchDB. The webmail interface will be developed
as a separate, optional component to maintain clean separation of concerns.

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

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

test/start-test-env.sh

@@ -63,5 +63,18 @@ echo ""
 echo "To run mail2couch:"
 echo "  cd ../go && ./mail2couch -config ../test/config-test.json"
 echo ""
+echo "📧 MAIL2COUCH DATABASE ACCESS:"
+echo "After running mail2couch, you can access the stored emails via CouchDB:"
+echo ""
+echo "📋 Database Access (examples after sync):"
+echo "  - All databases: http://localhost:5984/_all_dbs"
+echo "  - Specific database: http://localhost:5984/m2c_specific_folders_only"
+echo "  - All documents: http://localhost:5984/m2c_specific_folders_only/_all_docs"
+echo "  - Individual message: http://localhost:5984/m2c_specific_folders_only/INBOX_12"
+echo ""
+echo "🔍 Raw Data Access:"
+echo "  - Database info: http://localhost:5984/m2c_specific_folders_only"
+echo "  - Document with content: http://localhost:5984/m2c_specific_folders_only/INBOX_12"
+echo ""
 echo "To stop the environment:"
 echo "  ./stop-test-env.sh"