fix: [BUG] query rewriting error using JSON_EXTRACT - #722

Fixes #352

Root cause

Query rewriter rejects non-column projections over an indirection (subquery)

Changes

• In internal/stackql/astvisit/query_rewriting.go the indirection branch of the AliasedExpr visit only tolerated an unresolvable column name when it looked like a json_each value or was an OrExpr (isAnonymous). Any other projected expression whose inferred name is not a column of the subquery (a function whose leading argument is a literal or a nested function, arithmetic, scalar subquery, ...) hard-failed. isAnonymous is replaced by isExpressionProjection, which treats every projection that is not a bare *sqlparser.ColName as opaque to the indirection's column inventory: the untyped relational column carrying the already-rendered decorated expression is emitted and passed to the SQL backend, exactly as the pre-existing json_each escape hatch does. Bare column references that do not exist in the subquery still error as before. Two robot scenarios were added to test/robot/functional/stackql_function_projection.robot (the json_extract-over-subquery case, sqlite-gated, and a backend-agnostic literal-leading function projection).