Implement AHEAD, CS-PICK, CS-ROLL (Programming-Tools word set)

Three compile-time words for unstructured control flow:
- AHEAD: unconditional forward branch (code to THEN skipped)
- CS-PICK: duplicate control-flow stack entries (enables multi-exit loops)
- CS-ROLL: rotate control-flow stack entries (reorder IF/THEN resolution)

Also adds POSTPONE support for compile-time keywords (IF, UNTIL, etc.)
via a __CTRL__ host function and unified pending_actions queue.

Key design:
- LoopRestartIfFalse IR op desugars into nested If nodes for CS-PICK'd
  BEGIN+UNTIL patterns (multiple backward branches in one loop)
- Flat Block/BranchIfFalse/EndBlock IR ops for CS-ROLL'd IF/THEN
  patterns where structured If nesting would consume wrong flags
- First-iteration flag local for AHEAD-into-BEGIN patterns (PT8)

Enables 12th compliance test (compliance_tools): all 11+1 now pass.

crates/core/src/ir.rs

@@ -111,6 +111,17 @@ pub enum IrOp {
     },
     /// Return from current word.
     Exit,
+    /// Conditional restart of enclosing loop (used by CS-PICK'd BEGIN + UNTIL).
+    /// Pops flag; if false, restart the loop. Desugared into nested `If` before codegen.
+    LoopRestartIfFalse,
+
+    // -- Flat forward branches (for CS-ROLL'd IF/THEN patterns) --
+    /// Open a WASM `block`. `BranchIfFalse` can target this to skip to `EndBlock`.
+    Block(u32),
+    /// Pop flag; if false, branch to matching `EndBlock` with this label.
+    BranchIfFalse(u32),
+    /// Close the `block` with this label.
+    EndBlock(u32),
 
     // -- Return stack --
     /// Move to return stack: ( x -- ) ( R: -- x )