feat: JSON/JSONB validation, multi-column indexes, CTE execution, wire protocol column types

- Add fkJson to wire protocol with serialization/deserialization
- Validate JSON/JSONB on INSERT/UPDATE via std/json
- Send real column type metadata in wire protocol responses
- Update all 4 clients (Nim, Python, JS, Rust) for JSON and columnTypes
- Implement multi-column index parser (CREATE INDEX idx ON t(a, b))
- Add ciColumns to AST nkCreateIndex
- Build composite index keys as table.col1.col2 with val1|val2
- Support multi-column exact match in SELECT for AND chains
- Implement non-recursive CTE execution via ctx.cteTables materialization
- Add tkRecursive token and parse WITH RECURSIVE
- Fix test isolation: use temp dirs for JOIN, migration, and RLS tests
- All tests passing (0 failures)

src/barabadb/query/lexer.nim

@@ -67,6 +67,7 @@ type
     tkCase
     tkWhen
     tkWith
+    tkRecursive
     tkDistinct
     tkUnion
     tkIntersect
@@ -231,6 +232,7 @@ const keywords*: Table[string, TokenKind] = {
   "case": tkCase,
   "when": tkWhen,
   "with": tkWith,
+  "recursive": tkRecursive,
   "distinct": tkDistinct,
   "union": tkUnion,
   "intersect": tkIntersect,