feat: complete code formatting and linting compliance

- Fix all Rust clippy warnings with targeted #[allow] attributes for justified cases
- Implement server-side IMAP SEARCH keyword filtering in Go implementation
- Add graceful fallback from server-side to client-side filtering when IMAP server lacks SEARCH support
- Ensure both implementations use identical filtering logic for consistent results
- Complete comprehensive testing of filtering and attachment handling functionality
- Verify production readiness with proper linting standards for both Go and Rust

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

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

go/main.go

@@ -152,7 +152,7 @@ func processImapSource(source *config.MailSource, couchClient *couch.Client, dbN
 				continue
 			}
 		} else {
-			fmt.Printf("     DRY-RUN: Would sync mailbox %s with %d current UIDs (mode: %s)\n", 
+			fmt.Printf("     DRY-RUN: Would sync mailbox %s with %d current UIDs (mode: %s)\n",
 				mailbox, len(currentUIDs), source.Mode)
 		}
 
@@ -200,7 +200,7 @@ func processImapSource(source *config.MailSource, couchClient *couch.Client, dbN
 			fmt.Printf("     DRY-RUN: Would store %d messages from %s\n", len(messages), mailbox)
 			// Show sample of what would be stored
 			if len(docs) > 0 {
-				fmt.Printf("     DRY-RUN: Sample message ID: %s (Subject: %s)\n", 
+				fmt.Printf("     DRY-RUN: Sample message ID: %s (Subject: %s)\n",
 					docs[0].ID, docs[0].Subject)
 			}
 		}