Fix _meta field format for MCP spec compliance (#367)

## Summary

Updates the `_meta` field structure to be compliant with the MCP
specification by using proper `prefix/name` format for vendor
extensions.

### Changes

- **Registry metadata**: `io.modelcontextprotocol.registry` →
`io.modelcontextprotocol.registry/official`
- **Publisher metadata**: `publisher` →
`io.modelcontextprotocol.registry/publisher-provided`
- **Database migration**: Updates indexes to use new field paths
- **Updated all code**: Service layer, validators, tests, and seed data

### Format Before
```json
{
  "_meta": {
    "publisher": { "license": "MIT" },
    "io.modelcontextprotocol.registry": { "id": "...", "is_latest": true }
  }
}
```

### Format After
```json
{
  "_meta": {
    "io.modelcontextprotocol.registry/publisher-provided": { "license": "MIT" },
    "io.modelcontextprotocol.registry/official": { "id": "...", "is_latest": true }
  }
}
```

This resolves the naming collision with the planned top-level
`publisher` field and ensures compliance with MCP specification
requirements.

Fixes #356

internal/database/memory.go

@@ -103,11 +103,11 @@ func (db *MemoryDB) CreateServer(ctx context.Context, server *apiv0.ServerJSON)
 	}
 
 	// Get the ID from the registry metadata
-	if server.Meta == nil || server.Meta.IOModelContextProtocolRegistry == nil {
+	if server.Meta == nil || server.Meta.Official == nil {
 		return nil, fmt.Errorf("server must have registry metadata with ID")
 	}
 
-	id := server.Meta.IOModelContextProtocolRegistry.ID
+	id := server.Meta.Official.ID
 
 	db.mu.Lock()
 	defer db.mu.Unlock()
@@ -193,8 +193,8 @@ func (db *MemoryDB) matchesFilter(entry *apiv0.ServerJSON, filter *ServerFilter)
 
 // getRegistryID safely extracts the registry ID from an entry
 func (db *MemoryDB) getRegistryID(entry *apiv0.ServerJSON) string {
-	if entry.Meta != nil && entry.Meta.IOModelContextProtocolRegistry != nil {
-		return entry.Meta.IOModelContextProtocolRegistry.ID
+	if entry.Meta != nil && entry.Meta.Official != nil {
+		return entry.Meta.Official.ID
 	}
 	return ""
 }

internal/database/migrations/004_update_meta_field_format.sql

@@ -0,0 +1,11 @@
+-- Update database indexes to use new MCP spec compliant _meta field paths
+-- Data has been updated manually, only need to update indexes
+
+-- Drop old indexes that reference the old paths
+DROP INDEX IF EXISTS idx_servers_name_latest;
+DROP INDEX IF EXISTS idx_servers_updated_at;
+
+-- Create new indexes with updated paths
+CREATE INDEX idx_servers_name_latest ON servers ((value->>'name'), (value->'_meta'->'io.modelcontextprotocol.registry/official'->>'is_latest'))
+    WHERE (value->'_meta'->'io.modelcontextprotocol.registry/official'->>'is_latest')::boolean = true;
+CREATE INDEX idx_servers_updated_at ON servers ((value->'_meta'->'io.modelcontextprotocol.registry/official'->>'updated_at'));

internal/database/postgres.go

@@ -78,7 +78,7 @@ func (db *PostgreSQL) List(
 		if _, err := uuid.Parse(cursor); err != nil {
 			return nil, "", fmt.Errorf("invalid cursor format: %w", err)
 		}
-		whereConditions = append(whereConditions, fmt.Sprintf("(value->'_meta'->'io.modelcontextprotocol.registry'->>'id') > $%d", argIndex))
+		whereConditions = append(whereConditions, fmt.Sprintf("(value->'_meta'->'io.modelcontextprotocol.registry/official'->>'id') > $%d", argIndex))
 		args = append(args, cursor)
 		argIndex++
 	}
@@ -94,7 +94,7 @@ func (db *PostgreSQL) List(
 		SELECT value
 		FROM servers
 		%s
-		ORDER BY (value->'_meta'->'io.modelcontextprotocol.registry'->>'id')
+		ORDER BY (value->'_meta'->'io.modelcontextprotocol.registry/official'->>'id')
 		LIMIT $%d
 	`, whereClause, argIndex)
 	args = append(args, limit)
@@ -131,8 +131,8 @@ func (db *PostgreSQL) List(
 	nextCursor := ""
 	if len(results) > 0 && len(results) >= limit {
 		lastResult := results[len(results)-1]
-		if lastResult.Meta != nil && lastResult.Meta.IOModelContextProtocolRegistry != nil {
-			nextCursor = lastResult.Meta.IOModelContextProtocolRegistry.ID
+		if lastResult.Meta != nil && lastResult.Meta.Official != nil {
+			nextCursor = lastResult.Meta.Official.ID
 		}
 	}
 
@@ -147,7 +147,7 @@ func (db *PostgreSQL) GetByID(ctx context.Context, id string) (*apiv0.ServerJSON
 	query := `
 		SELECT value
 		FROM servers
-		WHERE (value->'_meta'->'io.modelcontextprotocol.registry'->>'id') = $1
+		WHERE (value->'_meta'->'io.modelcontextprotocol.registry/official'->>'id') = $1
 	`
 
 	var valueJSON []byte
@@ -177,11 +177,11 @@ func (db *PostgreSQL) CreateServer(ctx context.Context, server *apiv0.ServerJSON
 	}
 
 	// Get the ID from the registry metadata
-	if server.Meta == nil || server.Meta.IOModelContextProtocolRegistry == nil {
+	if server.Meta == nil || server.Meta.Official == nil {
 		return nil, fmt.Errorf("server must have registry metadata with ID")
 	}
 
-	id := server.Meta.IOModelContextProtocolRegistry.ID
+	id := server.Meta.Official.ID
 
 	// Marshal the complete server to JSONB
 	valueJSON, err := json.Marshal(server)
@@ -219,7 +219,7 @@ func (db *PostgreSQL) UpdateServer(ctx context.Context, id string, server *apiv0
 	query := `
 		UPDATE servers 
 		SET value = $1
-		WHERE (value->'_meta'->'io.modelcontextprotocol.registry'->>'id') = $2
+		WHERE (value->'_meta'->'io.modelcontextprotocol.registry/official'->>'id') = $2
 	`
 
 	result, err := db.conn.Exec(ctx, query, valueJSON, id)