fix: SQL SHOW TABLES/VIEWS and DESCRIBE fail for all drivers

The grammar rule used bare IDENTIFIER for the target in
SQL <alias> SHOW TABLES and SQL <alias> DESCRIBE <table>,
but TABLES, VIEWS etc. are dedicated lexer tokens that don't
match IDENTIFIER. The command fell through to the sqlQuery
passthrough rule, sending raw "SHOW TABLES" to the database
which fails on Oracle (ORA-00900) and SQL Server.

Changed to identifierOrKeyword which matches both identifiers
and keyword tokens. Updated visitor to use IdentifierOrKeyword()
accordingly.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ako

mdl/grammar/MDLParser.g4

@@ -2918,8 +2918,8 @@ sqlStatement
     : SQL CONNECT IDENTIFIER STRING_LITERAL AS IDENTIFIER          # sqlConnect
     | SQL DISCONNECT IDENTIFIER                                     # sqlDisconnect
     | SQL CONNECTIONS                                               # sqlConnections
-    | SQL IDENTIFIER SHOW IDENTIFIER                                # sqlShowTables
-    | SQL IDENTIFIER DESCRIBE IDENTIFIER                            # sqlDescribeTable
+    | SQL IDENTIFIER SHOW identifierOrKeyword                        # sqlShowTables
+    | SQL IDENTIFIER DESCRIBE identifierOrKeyword                   # sqlDescribeTable
     | SQL IDENTIFIER GENERATE CONNECTOR INTO identifierOrKeyword
       (TABLES LPAREN identifierOrKeyword (COMMA identifierOrKeyword)* RPAREN)?
       (VIEWS LPAREN identifierOrKeyword (COMMA identifierOrKeyword)* RPAREN)?

mdl/grammar/parser/MDLParser.interp

@@ -46,12 +46,12 @@ func (b *Builder) ExitSqlConnections(ctx *parser.SqlConnectionsContext) {
 
 // ExitSqlShowTables handles SQL <alias> SHOW TABLES|VIEWS|FUNCTIONS
 func (b *Builder) ExitSqlShowTables(ctx *parser.SqlShowTablesContext) {
-	ids := ctx.AllIDENTIFIER()
-	if len(ids) < 2 {
+	alias := ctx.IDENTIFIER().GetText()
+	iok := ctx.IdentifierOrKeyword()
+	if iok == nil {
 		return
 	}
-	alias := ids[0].GetText()
-	target := strings.ToUpper(ids[1].GetText())
+	target := strings.ToUpper(iok.GetText())
 
 	switch target {
 	case "VIEWS":
@@ -66,12 +66,12 @@ func (b *Builder) ExitSqlShowTables(ctx *parser.SqlShowTablesContext) {
 
 // ExitSqlDescribeTable handles SQL <alias> DESCRIBE <table>
 func (b *Builder) ExitSqlDescribeTable(ctx *parser.SqlDescribeTableContext) {
-	ids := ctx.AllIDENTIFIER()
-	if len(ids) < 2 {
+	alias := ctx.IDENTIFIER().GetText()
+	iok := ctx.IdentifierOrKeyword()
+	if iok == nil {
 		return
 	}
-	alias := ids[0].GetText()
-	table := ids[1].GetText()
+	table := iok.GetText()
 	b.statements = append(b.statements, &ast.SQLDescribeTableStmt{
 		Alias: alias,
 		Table: table,