Add DOES>, EVALUATE, double-cell arithmetic, and 20+ more Core words

- DOES> with split-compilation for defining words (CREATE , DOES> @ pattern)
- EVALUATE for string interpretation
- Double-cell: M* UM* UM/MOD FM/MOD SM/REM S>D */ */MOD
- Parsing: WORD FIND COUNT >NUMBER >IN STATE
- Memory: CMOVE CMOVE>
- Compile-time: ABORT" S" (compile mode)
- 219 tests passing, ~90% Core word set coverage
- Update docs to reflect current implementation

CLAUDE.md

@@ -53,5 +53,5 @@ Handle in `interpret_token_immediate()` or `compile_token()` as a special case.
 1. Correctness first, performance second
 2. Maximize Forth, minimize Rust (self-hosting goal -- not yet started)
 3. Test-driven: if it's not tested, it doesn't work
-4. Never break existing tests
-5. No Co-Authored-By or AI attribution in commits
+4. Every word set at 100% compliance before moving to the next
+5. Never break existing tests