fix: open-issue sweep — drawing, plot, snap, layout and UI fixes

Fixes:
- Font prompt no longer lists bundled ltypeshp/qcadshp shape files (#1626)
- Wide polylines step at a discontinuous segment width; PEDIT marks the
  current vertex; keyword steps refresh the command preview (#1628)
- Radius-0 fillet drops the zero-length segment it left, so the corner
  fillets again (#1422)
- FILLET Trim / No trim option (#1558)
- True-colour wires plot in their own colour; colour picker stores the
  value it shows (#1621)
- Model tab keeps its page setup; "Save changes to layout" in Model (#1620)
- QNEW default template in Options > Files; .dwt in the open dialog
  (#1134, #1113)
- GRIDUNIT / GRIDMODE / PERSPECTIVE variables (#1618, #1524)
- PTYPE (#1433)
- ZOOM nX / nXP (#1465)
- CHSPACE between model and paper space through a viewport (#1428)
- Moving a dimension keeps its automatic text placement
- Shell icon; "&&" button labels (#1554)
- LINETYPE Load from a .lin file (#1588)
- XLINE / RAY hide the crosshair arms (#1437)
- Dynamic-input boxes keep clear of the crosshair and each other (#1546)
- Snap marker colour setting, dark default on light canvases
  (#1497, #1229, #1128)
- Dimension style precision as a 0.00 pattern dropdown (#1426)
- Node graph nodes left of the origin no longer clip away (#1592)
- Collapse button in the command history header (#1094)
- Freeze-in-current-viewport toggle in the ribbon layer list (#1466)
- Geometric Center object snap for closed polylines (#1369)

New strings translated in all 21 locales.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

assets/icons/layers/layvpfrz.svg

@@ -0,0 +1,9 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" width="64" height="64">
+  <rect x="1.5" y="3.5" width="21" height="17" rx="1.5" fill="none" stroke="#8FA3B5" stroke-width="1.6"/>
+  <g stroke="#6DB7ED" stroke-width="1.8" stroke-linecap="round">
+    <line x1="12" y1="6.5" x2="12" y2="17.5"/>
+    <line x1="6.5" y1="12" x2="17.5" y2="12"/>
+    <line x1="8.1" y1="8.1" x2="15.9" y2="15.9"/>
+    <line x1="15.9" y1="8.1" x2="8.1" y2="15.9"/>
+  </g>
+</svg>

assets/icons/layers/layvpthw.svg

@@ -0,0 +1,10 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" width="64" height="64">
+  <rect x="1.5" y="3.5" width="21" height="17" rx="1.5" fill="none" stroke="#8FA3B5" stroke-width="1.6"/>
+  <circle cx="12" cy="12" r="2.6" fill="#f0c040" fill-opacity="0.4" stroke="#f0c040" stroke-width="1.6"/>
+  <g stroke="#f0c040" stroke-width="1.6" stroke-linecap="round">
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+    <line x1="12" y1="16.4" x2="12" y2="17.7"/>
+    <line x1="6.3" y1="12" x2="7.6" y2="12"/>
+    <line x1="16.4" y1="12" x2="17.7" y2="12"/>
+  </g>
+</svg>

assets/icons/model/shell.svg

@@ -0,0 +1,10 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32" role="img" aria-label="Shell">
+  <g stroke="#526B80" stroke-width="1.1" stroke-linejoin="round">
+    <path d="M8.5 10 15 6.6V14L8.5 17.4Z" fill="#526B80"/>
+    <path d="M15 6.6 23.5 10V17.4L15 14Z" fill="#3F5466"/>
+    <path d="M8.5 17.4 15 14 23.5 17.4 17 20.8Z" fill="#6DB7ED"/>
+    <path d="M4 10 17 16V28L4 22Z" fill="#A9BFCE"/>
+    <path d="M17 16 28 10V22L17 28Z" fill="#718C9E"/>
+    <path d="M4 10 15 4 28 10 17 16ZM8.5 10 15 6.6 23.5 10 17 13.4Z" fill="#DCE7F0" fill-rule="evenodd"/>
+  </g>
+</svg>

assets/icons/osnap/geometric_center.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="#B4B6B9" stroke-width="1.9" stroke-linecap="round" stroke-linejoin="round"><path d="M12 3.5 20.5 9.7 17.3 19.5H6.7L3.5 9.7Z"/><circle cx="12" cy="12.5" r="1.6" fill="#B4B6B9"/></svg>