Create boot.fth loaded at startup after IR primitives are compiled.
Forth-compiled WASM with direct calls outperforms host function dispatch
(no call_indirect overhead, Cranelift can inline across word boundaries).
Words moved to Forth: 2OVER, 2ROT, WITHIN, 2@, 2!, FILL, CMOVE, CMOVE>,
MOVE, ERASE, BLANK, /STRING, -TRAILING.
Removed 547 lines of Rust closures, replaced by 48 lines of Forth.
All 425 tests pass.
