feat(nodedb-sql): add typed DDL AST module

Introduce `nodedb_sql::ddl_ast` — a typed representation of every
NodeDB DDL statement as `NodedbStatement` enum variants, with a
whitespace-token parser that converts raw SQL into the typed form.

The AST gives DDL dispatch a compiler-checked match instead of
string-prefix branching, so adding a new DDL command forces handling
in every affected site at compile time rather than at runtime.

Author: farhan-syah

nodedb-sql/src/ddl_ast/mod.rs

@@ -0,0 +1,16 @@
+//! Typed AST for NodeDB-specific DDL statements.
+//!
+//! Every DDL command the system supports is represented as a variant
+//! of [`NodedbStatement`]. The DDL router matches on this enum
+//! instead of string prefixes, so the compiler catches missing
+//! handlers when a new DDL is added.
+//!
+//! The parser ([`parse`]) converts raw SQL into a `NodedbStatement`
+//! using whitespace-split token matching — the same technique the
+//! old string-prefix router used, but producing a typed output.
+
+pub mod parse;
+pub mod statement;
+
+pub use parse::parse;
+pub use statement::NodedbStatement;