refactor(core): remove old jit.ts and rename jit2.ts to jit.ts

Consolidate the JIT system to use only the unified expression tree
architecture. The old Context/Slot API is removed in favor of Builder/Ref.

Changes:
- Delete old jit.ts (Context, Slot, jit.fn pattern)
- Rename jit2.ts to jit.ts (Builder, Ref, fn pattern)
- Update core/index.ts exports
- Migrate change-detector.ts, snapshot.ts, path.ts to new API
- Migrate benchmark files to new API
- Update compat.ts documentation

All 1949 type package tests passing.

Author: marcj

packages/core/index.ts

@@ -18,64 +18,6 @@ export * from './src/network.js';
 export * from './src/perf.js';
 export * from './src/compiler.js';
 export * from './src/jit.js';
-// jit2 exports - Builder API for unified expression trees (JIT + Exec)
-// Note: Some exports overlap with jit.js (Arg, canJIT, etc.), so we selectively export
-export {
-    // Expression tree types
-    type LitExpr,
-    type InputExpr,
-    type VarExpr,
-    type GetExpr,
-    type AtExpr,
-    type CallExpr,
-    type NewExpr,
-    type ObjExpr,
-    type ArrExpr,
-    type EqExpr,
-    type NeqExpr,
-    type LtExpr,
-    type GtExpr,
-    type LteExpr,
-    type GteExpr,
-    type NotExpr,
-    type AndExpr,
-    type OrExpr,
-    type NullishExpr,
-    type TypeofExpr,
-    type IsTypeExpr,
-    type IsNullExpr,
-    type IsNullishExpr,
-    type HasExpr,
-    type LenExpr,
-    type TernaryExpr,
-    type InstanceofExpr,
-    type ConcatExpr,
-    type MapExpr,
-    type Expr,
-    // Statement types
-    type LetStmt,
-    type SetStmt,
-    type PushStmt,
-    type SetVarStmt,
-    type ExecStmt,
-    type ReturnStmt,
-    type ThrowStmt,
-    type IfStmt,
-    type LoopStmt,
-    type ForInStmt,
-    type SwitchStmt,
-    type Stmt,
-    type Block,
-    // Core classes
-    Ref,
-    VarRef,
-    Builder,
-    // Functions
-    arg,
-    fn,
-    fnJIT,
-    fnExec,
-} from './src/jit2.js';
 export * from './src/string.js';
 export * from './src/emitter.js';
 export * from './src/reactive.js';