继续按 align-linuxcnc 约束：补只读命名参数源回归

结论：新增 LinuxCNC-backed readonly named parameter fixture，依据 interp_namedparams.cc::lookup_named_param 与 init_readonly_param，在 native librs274 与 source-link runner 中验证 #<_metric>/#<_imperial>/#<_absolute>/#<_incremental>/#<_feed>/#<_rpm>/#<_spindle_on>/#<_spindle_cw>；未扩展 smoke，test-native 与 test-linuxcnc-source-link 均通过。

test-native.sh

@@ -145,6 +145,8 @@ grep -F 'convert_lathe_diameter_mode() scales G7/G8 X words and G76 I/J/K words'
 grep -F 'tests/gcode/linuxcnc_lathe_diameter_mode.ngc' docs/linuxcnc-porting.md >/dev/null
 grep -F 'tests/gcode/linuxcnc_lathe_diameter_g76.ngc' docs/linuxcnc-porting.md >/dev/null
 grep -F 'missing source-linked G7 diameter-mode G76 final threading pass' test-linuxcnc-source-link.sh >/dev/null
+grep -F 'lookup_named_param()' test-linuxcnc-rs274-native.sh >/dev/null
+grep -F 'tests/gcode/linuxcnc_readonly_named_parameters.ngc' docs/linuxcnc-porting.md >/dev/null
 grep -F 'rs274ngc_pre.cc ini_load() consumes INI_FILE_NAME' test-web-wasm-node-smoke.cjs >/dev/null
 grep -F 'rs274ngc_pre.cc ini_load() consumes INI_FILE_NAME' web/test-browser-wasm-smoke-linuxcnc-sections.js >/dev/null
 grep -F 'metadata:src/emc/nml_intf/emcops.cc:source basis for native source-link EMC status constructor support object' linuxcnc-rs274-source-files.txt >/dev/null