Attach Underlay ribbon menu, DWF/DGN attach dialog, DGN true colours

- Insert > Reference: the PDF Attach button becomes an Attach Underlay menu
  (PDF / DWF / DGN); its face runs the last one chosen.
- DWFATTACH, DGNATTACH and ATTACH on a .dwf/.dwfx/.dgn open the Attach
  dialog for that kind: sheets or models with thumbnails (one chosen),
  placement, path type, file details with the sheet / model size, and for
  DGN the conversion units (sub units offer 1 / sub units per master as the
  scale).
- DGN V8 true colours come from the ExtendedColors record packed in the
  non-model attributes stream; the colour word's high part numbers them.
- A DGN model's extent includes each text's box (its length along the
  baseline and 1.5 x its height), as the reference sizes a model.
- DWFx text uses the family named in its embedded (deobfuscated) font.
- DWF contrast pivots at 0.73 once colours are turned over for a dark
  background.
- Hairline strokes are drawn solid one pixel wide, and underlay rasters are
  made at or below their size on screen so those lines stay unbroken.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

locales/ru-RU/opencadstudio.ftl

@@ -3553,6 +3553,25 @@ insert =
     .pdfui-search-for-layer = Search for layer
     .pdfui-reference-name = Reference name:
     .pdfui-page-size = Page size:
+    .ul-attach-underlay = Attach Underlay
+    .ul-attach-dwf = Attach DWF
+    .ul-attach-dgn = Attach DGN
+    .ul-attach-dwf-underlay = Attach DWF Underlay
+    .ul-attach-dgn-underlay = Attach DGN Underlay
+    .ul-sheet-count = __ocs_fmt_0__ sheets
+    .ul-model-count = __ocs_fmt_0__ models
+    .ul-sheets = Sheets
+    .ul-models = Models
+    .ul-selected-sheet = Selected sheet: __ocs_fmt_0__
+    .ul-selected-model = Selected model: __ocs_fmt_0__
+    .ul-sheet-size = Sheet size:
+    .ul-model-size = Model size:
+    .ul-conversion-units = Conversion units
+    .ul-master-units = Master units
+    .ul-sub-units = Sub units
+    .ul-sub-units-scale = Sub units make the default scale __ocs_fmt_0__
+    .ul-attaches-dwf = Attaches a DWF or DWFx file as an underlay.
+    .ul-attaches-dgn = Attaches a DGN file as an underlay.
     .pdfui-select-one-or-more-pages-from-the-pdf-file = Select one or more pages from the PDF file:
     .pdfui-import-pdf = Import PDF
     .pdfui-pdf-import-settings = PDF Import Settings