增加G90G91批量fixture验证

结论：新增 modal_incremental fixture，覆盖 G90/G91 距离模式切换、G1 模态继承和回到绝对模式；验证脚本改为批量执行所有 G-code fixture 并匹配 expected canonical events。检查：git diff --check 通过；wasm-port/tests/native/verify_native_probes.sh 通过。

wasm-port/docs/porting-steps-standalone.md

@@ -354,6 +354,12 @@ Current verified progress:
 - The same validation is now fixture-driven through
   `tests/fixtures/gcode/minimal_linear.ngc` and
   `tests/fixtures/canon/minimal_linear.events`.
+- `tests/fixtures/gcode/modal_incremental.ngc` and
+  `tests/fixtures/canon/modal_incremental.events` add `G90`/`G91`
+  distance-mode switching plus modal `G1` carry-forward coverage. The
+  temporary wrapper behavior is based on LinuxCNC
+  `interp_convert.cc::convert_distance_mode()` and
+  `interp_convert.cc::convert_straight()`.
 - This proves the current extracted interpreter slice can parse and execute a
   simple traverse and feed move through a standalone canonical event sink.
 
@@ -654,8 +660,9 @@ Keep these documents under `wasm-port/docs/`:
 Continue expanding the standalone interpreter core from the verified minimal
 traverse path:
 
-1. add another fixture for incremental mode and modal carry-forward,
-2. replace the temporary minimal `convert_g()` implementation with thin
+1. replace the temporary minimal `convert_g()` implementation with thin
    wrappers around more vendored interpreter conversion code,
+2. add fixture coverage for `Z` moves and multi-axis current-position
+   parameter updates,
 3. keep all source changes inside `wasm-port/` and leave `../linuxcnc/`
    read-only.