feat: Phase 2 - Add DDL operations and real MQ broker integration

Implements comprehensive DDL support for MQ topic management:

New Components:
- Real MQ broker connectivity via BrokerClient
- CREATE TABLE → ConfigureTopic gRPC calls
- DROP TABLE → DeleteTopic operations
- DESCRIBE table → Schema introspection
- SQL type mapping (SQL ↔ MQ schema types)

Enhanced Features:
- Live topic discovery from MQ broker
- Fallback to cached/sample data when broker unavailable
- MySQL-compatible DESCRIBE output
- Schema validation and error handling
- CREATE TABLE with column definitions

Key Infrastructure:
- broker_client.go: gRPC communication with MQ broker
- sql_types.go: Bidirectional SQL/MQ type conversion
- describe.go: Table schema introspection
- Enhanced engine.go: Full DDL routing and execution

Supported SQL Operations:
✅ SHOW DATABASES, SHOW TABLES (live + fallback)
✅ CREATE TABLE table_name (col1 INT, col2 VARCHAR(50), ...)
✅ DROP TABLE table_name
✅ DESCRIBE table_name / SHOW COLUMNS FROM table_name

Known Limitations:
- SQL parser issues with reserved keywords (e.g., 'timestamp')
- Requires running MQ broker for full functionality
- ALTER TABLE not yet implemented
- DeleteTopic method needs broker-side implementation

Architecture Decisions:
- Broker discovery via filer lock mechanism (same as shell commands)
- Graceful fallback when broker unavailable
- ConfigureTopic for CREATE TABLE with 6 default partitions
- Schema versioning ready for ALTER TABLE support

Testing:
- Unit tests updated with filer address parameter
- Integration tests for DDL operations
- Error handling for connection failures

Next Phase: SELECT query execution with Parquet scanning

weed/command/sql.go

@@ -50,7 +50,7 @@ func runSql(command *Command, args []string) bool {
 
 	// Initialize SQL engine
 	// Assumption: Engine will connect to MQ broker on demand
-	sqlEngine := engine.NewSQLEngine()
+	sqlEngine := engine.NewSQLEngine(*sqlServer)
 
 	// Interactive shell loop
 	scanner := bufio.NewScanner(os.Stdin)