add auto dxf units import

src/kiri/app/platform.js

@@ -1156,7 +1156,7 @@ function loadDXFDialog(doit) {
         `  Supports POLYLINE, LWPOLYLINE, LINE, CIRCLE, ARC, and SPLINE entities.`,
         `  </p>`,
         `  <div class="f-row t-right image-convert-fields"><table>`,
-        `  <tr><th>units</th><td><select id="dxf-units-${rnd}"><option value="mm">millimeters</option><option value="inch">inches</option></select></td></tr>`,
+        `  <tr><th>units</th><td><select id="dxf-units-${rnd}"><option value="auto" selected>auto</option><option value="mm">millimeters</option><option value="inch">inches</option></select></td></tr>`,
         `  <tr><th>z height</th><td><input id="dxf-depth-${rnd}" value="5" size="3"></td></tr>`,
         `  <tr><th title="target length of each line segment when converting arcs and circles">arc segment size</th><td><input id="dxf-seg-${rnd}" value="1" size="3"></td></tr>`,
         `  <tr><th title="minimum number of segments for very small arcs to avoid degenerate geometry">minimum arc segments</th><td><input id="dxf-min-${rnd}" value="4" size="3"></td></tr>`,

src/load/dxf.js

@@ -26,9 +26,10 @@ export function parse(text, opt = { }) {
     // Parse DXF file - normalize line endings and split
     const lines = text.replace(/\r\n/g, '\n').replace(/\r/g, '\n').split('\n').map(l => l.trim());
 
-    // Parse header for units (informational, can be overridden by user)
+    // Parse header for units (can be overridden by user)
     const fileUnits = extractUnits(lines);
-    const inputUnits = opt.units || fileUnits; // user can override file's declared units
+    // Use file units if "auto" or not specified, otherwise use user's choice
+    const inputUnits = (!opt.units || opt.units === 'auto') ? fileUnits : opt.units;
     const scale = getScaleToMM(inputUnits); // convert to mm (Kiri:Moto's internal unit)
 
     const entities = extractEntities(lines);