增加G1零进给错误fixture验证

结论：新增 g1_zero_feed 负向 fixture，固定 G1 在 feed rate 为 0 时返回 INTERP_ERROR=5、输出 LinuxCNC 对应错误文本、不产生 STRAIGHT_FEED，且失败前不更新当前位置和 #5420/#5421/#5422。检查：git diff --check 通过；wasm-port/tests/native/verify_native_probes.sh 通过。

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

@@ -365,6 +365,11 @@ Current verified progress:
   current-position parameter visibility for `#5420`, `#5421`, and `#5422`.
   The parameter source basis is LinuxCNC
   `interp_parameter_def.hh` and `interp_namedparams.cc`.
+- `tests/fixtures/gcode_errors/g1_zero_feed.ngc` and
+  `tests/fixtures/canon_errors/g1_zero_feed.expected` pin the negative
+  `G1` zero-feed case. The source basis is LinuxCNC
+  `interp_convert.cc::convert_straight()` and
+  `rs274ngc_return.hh::NCE_CANNOT_DO_G1_WITH_ZERO_FEED_RATE`.
 - This proves the current extracted interpreter slice can parse and execute a
   simple traverse and feed move through a standalone canonical event sink.
 
@@ -667,7 +672,7 @@ traverse path:
 
 1. replace the temporary minimal `convert_g()` implementation with thin
    wrappers around more vendored interpreter conversion code,
-2. add a negative fixture for `G1` without feed rate to start pinning error
-   semantics,
+2. add `_x`/`_y`/`_z` named parameter fixture coverage and align it with
+   `#5420`/`#5421`/`#5422`,
 3. keep all source changes inside `wasm-port/` and leave `../linuxcnc/`
    read-only.