fix: implement server-side folder filtering using IMAP LIST patterns

Replace client-side wildcard filtering with IMAP LIST pattern matching
for improved efficiency and accuracy. This fixes the issue where patterns
like "Work*" were not matching folders like "Work/Projects".

Key improvements:
- Use IMAP LIST with patterns for server-side filtering
- Remove dependency on doublestar library
- Add ListFilteredMailboxes() method with proper IMAP pattern support
- Remove obsolete ShouldProcessMailbox() client-side filtering
- Significantly reduce network traffic by filtering at server

This ensures the Go implementation correctly processes folder patterns
and achieves feature parity with the Rust implementation.

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

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

go/main.go

@@ -66,12 +66,13 @@ func processImapSource(source *config.MailSource, couchClient *couch.Client, dbN
 
 	fmt.Println("   IMAP connection successful.")
 
-	mailboxes, err := imapClient.ListMailboxes()
+	// Use IMAP LIST with patterns for server-side filtering
+	mailboxes, err := imapClient.ListFilteredMailboxes(&source.FolderFilter)
 	if err != nil {
-		return fmt.Errorf("failed to list mailboxes: %w", err)
+		return fmt.Errorf("failed to list filtered mailboxes: %w", err)
 	}
 
-	fmt.Printf("   Found %d mailboxes.\n", len(mailboxes))
+	fmt.Printf("   Found %d matching mailboxes after filtering.\n", len(mailboxes))
 
 	// Parse the since date from config if provided (fallback for first sync)
 	var configSinceDate *time.Time
@@ -87,14 +88,8 @@ func processImapSource(source *config.MailSource, couchClient *couch.Client, dbN
 	totalMessages := 0
 	totalStored := 0
 
-	// Process each mailbox
+	// Process each mailbox (already filtered by IMAP LIST)
 	for _, mailbox := range mailboxes {
-		// Check if this mailbox should be processed based on filters
-		if !imapClient.ShouldProcessMailbox(mailbox, &source.FolderFilter) {
-			fmt.Printf("   Skipping mailbox: %s (filtered)\n", mailbox)
-			continue
-		}
-
 		fmt.Printf("   Processing mailbox: %s (mode: %s)\n", mailbox, source.Mode)
 
 		// Get sync metadata to determine incremental sync date