aliases: import AutoCAD PGP files and support UCS-follow workflows

docs/pgp-import.md

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+# Importing AutoCAD command aliases (.pgp)
+
+1. Run `ALIASEDIT` in OpenCADStudio.
+2. Choose **Import PGP…** and select an AutoCAD or OpenCAD `.pgp` file.
+3. Review the working rows. Supported imported aliases override matching
+   existing aliases; other existing aliases are retained.
+4. Choose **Apply** to activate and save the rows, or close and discard them.
+
+There is no automatic discovery or loading of AutoCAD profiles. Importing only
+changes the editor's working rows; it never changes the active table until
+Apply. The source PGP is not modified.
+
+## Format and compatibility
+
+- UTF-8 (with or without BOM) and legacy Windows-1252 are accepted.
+- `;` comments, whitespace padding and case-insensitive names are supported.
+- The last definition of an alias wins, including user overrides at the end.
+- Common Spanish command targets are translated, for example `COPIA` to
+  `COPY`, `EMPALME` to `FILLET` and `SCP` to `UCS`. Alias keys are not translated.
+- Only registered command targets are imported. Unsupported commands and
+  unmapped translations are counted in the editor's summary and do not replace
+  existing aliases. Full diagnostics are logged, rather than flooding the
+  command line with errors. This does not implement missing AutoCAD/Civil 3D
+  commands or add support for every AutoCAD language.
+- External-program definitions are ignored and never executed.
+
+## Synthetic example
+
+This minimal example is authored for testing, not copied from an Autodesk PGP:
+
+```text
+; Last definition wins; imported aliases remain drafts until Apply.
+E, *BORRA
+E, *EMPALME
+CC, *COPIA
+SQ, *SCP
+```
+
+After importing, `E` resolves to `FILLET`, `CC` to `COPY`, and `SQ` to `UCS`.
+No proprietary PGP or user profile is included with this feature.