feat: implement per-account databases and native CouchDB attachments

- Create separate CouchDB database for each mail source (account)
- Store email attachments as native CouchDB attachments
- Add GenerateAccountDBName() for CouchDB-compatible database naming
- Update MailDocument structure to support _attachments field
- Implement StoreAttachment() for CouchDB attachment API
- Add placeholder attachment testing for every 3rd message

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

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

go/main.go

@@ -23,25 +23,30 @@ func main() {
 		log.Fatalf("Failed to create CouchDB client: %v", err)
 	}
 
-	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
-	defer cancel()
-
-	err = couchClient.EnsureDB(ctx, cfg.CouchDb.Database)
-	if err != nil {
-		log.Printf("Could not ensure CouchDB database exists (is it running?): %v", err)
-	} else {
-		fmt.Printf("CouchDB database '%s' is ready.\n", cfg.CouchDb.Database)
-	}
-
 	fmt.Printf("Found %d mail source(s) to process.\n", len(cfg.MailSources))
 	for _, source := range cfg.MailSources {
 		if !source.Enabled {
 			continue
 		}
 
+		// Generate per-account database name
+		dbName := couch.GenerateAccountDBName(source.Name, source.User)
+		
+		// Ensure the account-specific database exists
+		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+		err = couchClient.EnsureDB(ctx, dbName)
+		cancel()
+		
+		if err != nil {
+			log.Printf("Could not ensure CouchDB database '%s' exists (is it running?): %v", dbName, err)
+			continue
+		} else {
+			fmt.Printf("CouchDB database '%s' is ready for account: %s\n", dbName, source.Name)
+		}
+
 		fmt.Printf(" - Processing source: %s\n", source.Name)
 		if source.Protocol == "imap" {
-			err := processImapSource(&source, couchClient, cfg.CouchDb.Database)
+			err := processImapSource(&source, couchClient, dbName)
 			if err != nil {
 				log.Printf("   ERROR: Failed to process IMAP source %s: %v", source.Name, err)
 			}
@@ -112,11 +117,11 @@ func processImapSource(source *config.MailSource, couchClient *couch.Client, dbN
 			docs = append(docs, doc)
 		}
 
-		// Store messages in CouchDB
+		// Store messages in CouchDB with attachments
 		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
 		stored := 0
-		for _, doc := range docs {
-			err := couchClient.StoreMessage(ctx, dbName, doc)
+		for i, doc := range docs {
+			err := couchClient.StoreMessage(ctx, dbName, doc, messages[i])
 			if err != nil {
 				log.Printf("     ERROR: Failed to store message %s: %v", doc.ID, err)
 			} else {